On the morning of Jan. 4, 2000, Bill Belichick began one of the biggest days in his professional life on a treadmill in the New York Jets' weight room. There was nothing unusual about that; he was among a handful of coaches who liked to work up a sweat before attacking the daily grind of the NFL.

What happened next, though, was hardly routine.

After his workout, Belichick -- still in his Jets warm-up suit -- was spotted leaving the building in an overcoat, carrying a briefcase.

"I said to myself, 'That is one of the strangest things I've ever seen. There's something up,'" former Jets public relations director Frank Ramos recalled of Belichick's unusual garb and oddly timed exit.

Something was up.

A few hours later, Belichick delivered one of the most stunning announcements in sports history. Moments before he was to be formally introduced as the Jets' coach, he famously scribbled on a sheet of loose-leaf paper that he was resigning as the "HC of the NYJ." He handed it to team officials and conducted a 50-minute news conference that went over like fingernails on a chalkboard.

What happened that day forever changed the Jets, the New England Patriots and the NFL. Twenty years later, it still evokes a variety of reactions from those involved -- anger, laughter, bewilderment, vindication and paranoia.

Some harbor conspiracy theories, believing Belichick was in cahoots with the Patriots before quitting on the Jets and his mentor, Bill Parcells. That he briefly left the building with a briefcase triggers images of clandestine and improper activity.

On some level, Belichick's departure is still shrouded in mystery. Some people, mainly in the Belichick camp, refuse to this day to talk about what they know. Responding to ESPN's interview requests, they acted as if they were being asked to snitch on a mob boss.

"Doubt I'll touch that one!" one longtime Belichick confidant said in a Facebook message to ESPN.

Former Jets president Steve Gutman, who followed Belichick at the podium during the infamous news conference, sounded like a witness under cross-examination when questioned about Belichick's resignation. Parcells, whose complex relationship with Belichick began in 1979 with the New York Giants and became the subject of an ESPN 30 for 30 documentary, recounted the day ever so carefully, as if walking barefoot near shattered glass.

In a way, that's just what it is.

Everybody knows the epilogue -- Belichick has become a six-time Super Bowl champion in New England, the Jets continue to wallow as an also-ran -- but there's more to the story. Here's a closer look at the 48-hour period that changed everything, through the eyes of those who were there:

On Sunday, Jan. 2, the Jets finished the 1999 season with an 8-8 record, defeating the Seattle Seahawks for their fourth straight win. With speculation swirling about his future, Parcells called an impromptu staff meeting at 9 a.m. Monday.

Bill Muir, Jets offensive line coach: "I can remember after our last game, we were all sitting in the office and the secretary came down and said Bill [Parcells] wanted to see everybody in the staff room. We all went in, we were sitting around the table. Bill comes in and he sits down and he says, 'Last night, after the game, I submitted my resignation to Steve Gutman. Due to a previous contractual commitment, Bill Belichick is now the head football coach.' He basically got up and left the room. It was pretty abrupt."

Parcells: "He was under contract to be the coach of the Jets if I wasn't there. That's just the way it was."

Gutman: "He had a contract and it was all set."

Muir: "[Parcells] left and, obviously, there's stoned, stunned silence in the room. I remember distinctly, Bill Belichick said, 'You guys probably figure I knew that, and that this was the logical conclusion, but I'm hearing it for the first time just like you.'"

In his book about the 1999 season, titled, "The Final Season," Parcells says he informed Belichick the day before the last game that he was "pretty sure" about retiring. He quotes Belichick's response as, "I've been waiting a year [to take over]."

Parcells told ESPN recently: "No, I don't remember that. I'm sure we talked about something at that point, but I don't remember the conversation."

Ramos, Jets public relations director: "On Monday, I had gone to Parcells early in the morning and gave him my idea how [his farewell news conference] would go. He would announce he would no longer be coaching, but would still be the executive in charge of the football operation, and that he would introduce Belichick to be the next football coach.

"It would be like a perfect pass, one coach to another. And [Parcells] said, 'Why don't you go talk to Bill about it?' So I did, and he wanted no part of it. Belichick said to me, 'No, let Bill have his day. He deserves the day, let him have that. I'll do it tomorrow.' I said, 'That's not how it should be. Bill has had a lot of big days and doesn't really need another big day. This would be a very smooth transition.'"

Carl Banks, Jets director of player development: "Given the history of that relationship -- I mean, the Giants' situation before -- it doesn't surprise that Belichick didn't want to be in the room for some kind of formal baton passing."

Ramos: "In my head, I thought there's something amiss here. When Bill Parcells runs something, he runs it. For him to not to want to say this is how it's going to be done, and to leave it to me to talk to Belichick ... I thought it was really strange."

Muir: "I remember later [on Monday], we were all sitting around waiting for Bill [Belichick] to call a meeting. Word came down the hall there won't be any meeting today. See you tomorrow. We all went home and we came back the next day."

Belichick did find time Monday to meet with Jets contract negotiator Mike Tannenbaum to discuss the team's salary-cap situation. Monday ended with Parcells' emotional farewell in the team auditorium. (His retirement from the NFL would be short-lived, as he returned to coach the Dallas Cowboys in 2003.) Earlier in the day, the Jets had received a fax from the Patriots, requesting to speak with Belichick about their head-coaching vacancy.

The Jets, who denied permission that day, scheduled a news conference for 2:30 p.m. Tuesday to introduce Belichick, who was first seen at 6 a.m. in the weight room on his fateful day. Belichick jogged on the treadmill alongside safety Kevin Williams, whom he later referenced in his rambling resignation speech. At the time, Williams was on injured reserve, recovering from a life-threatening bacterial infection that had left him in a coma for two weeks.

Williams: "I was just walking on the treadmill -- they wouldn't let me jog or anything yet -- and [Belichick] came in and did his run. He was kind of sad. You could tell something was on his mind. We could see outside over the fields, and he said something like, 'All you can keep doing is working hard.' It was kind of philosophical, like, 'You can work as hard as you can work and sometimes it seems like it ain't good enough.'"

Banks: "I was one of the last people who spoke with [Belichick] prior to that announcement. He was down in the gym, working out on the treadmill. I literally walked up to him and I said, 'Congratulations, do you need me to do anything today?' He just kind of looked at me and said, 'No, I won't need anything. Thanks, Carl.' He gave no indication. I mean, it was as straight face as you could get."

Then, according to Ramos, Belichick slipped out of the building briefly and suspiciously in his overcoat.

Ramos: "I told Steve Gutman about it. I said, 'This is really unusual. You can't believe what I just saw.' He said, 'Gee, I have no idea what that means.'

"Obviously, he had gone to make a phone call off the property, or something like that. Maybe he had a contract in hand. My feeling was, he had a contract in hand on Saturday. I don't know that to be true, but that was my feeling, that he already knew that Parcells was going to retire as football coach and that he and [Patriots owner Robert] Kraft had already put together a package."

Victor Green, Jets safety: "When I got done lifting, I went up to Belichick's office and gave him a Tiffany paperweight for his desk, a congratulatory gift. It was so nice. It was like a snow globe, shaped like that. It was crystal. He took it, he thanked me. It was like nothing went down or was going down."

Dan Henning, Jets quarterbacks coach: "[Belichick] called a meeting and we sat around, and he talked about what we were going to do for the next six weeks, like going to the Senior Bowl. Which was fine. He was the head coach. Business as usual. That's the way I saw it."

Parcells (from his book) : "From what I learned later, Belichick was not the same guy on Tuesday that he was on Monday. He was visibly nervous. He couldn't stop his hands from shaking in the coaches' meeting, which he called to an early halt."

Muir: "I remember leaving the room and calling my wife and saying, 'I think I need to go look for a job.'"

Mary Grace Tranchina, executive assistant to the coaching staff: "The coaches' locker room was right across from my office and [Belichick] came out of the locker room freshly showered, but disheveled as could be. Like, I don't know, it was strange. Looking back now, it makes sense now, but I never knew."

Muir: "I left the building to go get a haircut. I came back in the building and everybody was glued to their TV. I said, 'What the hell is going on?'"

Henning, hired by Parcells, not Belichick, walked to Parcells' office to discuss his job status. He wondered if Belichick would retain him.

Henning: "[Parcells] said, 'Sit down, you may not have to do anything.' I said, 'What are you talking about?' He said, 'Watch the TV.' So I was sitting in there with Bill, watching the TV, when Belichick had the press conference and resigned. I said, 'How did that all happen?' He said, 'Well, you know, he apparently has something going with another team.' Obviously, New England."

Parcells: "[I found out] that day, I guess. He came in and had a piece of paper in his hand and said he was resigning the job."

Gutman: "Two words: Surprise and disappointment."

Parcells: "I don't know [if I was surprised]. I was just disappointed, I guess."

Gutman: "I found out that minute -- as he walked into the press conference."

Ramos opened the news conference this way: "At this time, I'd like to introduce Bill Belichick, who has an announcement to make." Belichick walked to the podium, giving a friendly hello as he sauntered past a reporter in the front row. With his shirt collar and tie knot askew, Belichick looked as if he had speed-dressed for the occasion.

Marvin Jones, Jets linebacker: "I remember watching the press conference with his wrinkled suit."

Williams: "I remember getting off the treadmill and going in the training room, and we were sitting in there talking, and it came across the screen, across ESPN, that he resigned. I just saw him! I could tell he had something on his mind, but he didn't say anything about that. He acted on instinct. He made up his mind, I guess, down there, and he went upstairs and did what he had to do."

Banks: "I was on the Belt Parkway [in New York], driving home. I was listening to it on the radio and it was like, 'Wow, I had no idea. I just talked to him.'"

Sal Paolantonio, ESPN reporter: "I was close to the center of the room [during the news conference], right in front. I could see everybody's faces. I could see Steve Gutman and he was ashen-faced, like somebody just told him that he lost his dog. Belichick walked up to the podium and he looked unhinged. He looked like he was extremely upset and I didn't know what the heck was going on."

Keyshawn Johnson, Jets wide receiver: "I was standing along the wall in the back of the room. I was blindsided. I was like, damn, how did that happen? He writes it on a [loose-leaf] napkin and basically says he's resigning. At that point, I'm walking down the hallway. I'm asking questions to assistant coaches, like, 'What are we going to do?' They didn't have any answers. It kind of got out of control."

Tranchina: "I was in the back of the auditorium ... and my jaw was to the ground."

Henning (who was watching in Parcells' office): "[Parcells'] reaction was like he was watching game film, trying to understand everything that was going on. Bill had responsibilities on both ends of it. Here's a guy that worked for him, he worked with for years and years. He knew there was going to be a tremendous outcry from both ends."

Parcells: "I don't recall too much. Your mind is on other things at the time when that was going on. I don't have a real clear recollection of that."

Gutman: "Surprise and disappointment. I keep saying the same thing because that's what it was."

After a 25-minute opening statement, followed by a Q&A with reporters, Belichick yielded the podium to Gutman and left the auditorium. Gutman told the reporters in attendance for the news conference: "We should have some feelings of sorrow and regret for him and his family. He obviously has some inner turmoil."

Ramos: "You could tell by his speech, Steve was really, really angry."

Belichick (in the ESPN documentary): "Essentially, the problem I had with the whole arrangement eventually was, when all this transpired, there was no owner. Mr. [Leon] Hess passed away before the '99 season. There were two potential owners, and that was [Woody] Johnson and [Charles] Dolan. I hadn't spoken with either one, but I had issues with both. It wasn't Mr. Hess anymore, which was the original agreement. ... That whole ownership configuration at that time was a major factor in my decision."

(Belichick declined ESPN's interview request for this story.)

Parcells (in his book): "His excuse about things changing with the death of Mr. Hess was weak."

Keyshawn Johnson: [The Parcells-Belichick relationship] soured. Yeah, you could tell there was some sort of -- I don't know -- tension. I think he did it because he didn't want Parcells hovering over the top of him, trying to control what he wanted to do with the team. They're boys now."

Parcells: "[Belichick has] kind of told me what his feelings were on it. Not quite then, but after that. It took a little while. That gave me a little different point of view. I was disappointed. I'm sure I told him that, and that was that. That's the way life is. It doesn't always go the way it's supposed to."

Paolantonio: "It's almost like a guy who, at the last minute, says, 'I can't marry this girl. It's not going to work for me and I know I'm going to upset a lot of people. I'm going to upset this woman, I'm going to upset her family, and everybody close to her. I paid for the tuxes and the flowers and the dance hall, everything, but this isn't the right thing for me to do.'"

Green: "He probably doesn't have the Tiffany paperweight anymore because it had 'Jets' on it. [Laughs.] He probably gave it away to someone at this point."

Paolantonio: "I hope somebody has that piece of paper [the "HC of the NYJ" resignation]. I hope when he goes into the Pro Football Hall of Fame, it's part of the Bill Belichick exhibit. It should be an important part of his historical documents. It's akin to having Richard Nixon's letter of resignation."

Alas, the paper apparently is lost. No one knows what happened to it. What they do remember is a certain newspaper headline.

The next morning, a Jets staffer clipped the New York Post back page and posted it on the bulletin board in the coaches' wing. It screamed, "Belichicken!" It stayed up for 24 hours, drawing laughs from Belichick's former colleagues.

A legal battle ensued between the Jets and Belichick, who tried -- unsuccessfully -- to void his contract with the team. It revived the so-called Border War between the Jets and Patriots, who clashed in 1997 when Parcells escaped his New England contract to join the Jets.

This time, Parcells and Kraft -- bitter rivals --- negotiated a compensation package. The Jets traded the rights to Belichick for a 2000 first-round pick, along with late-round swaps. Then linebackers coach for the Jets, Al Groh was named New York's head coach for the 2000 season.

The Patriots said they did everything by the book, but some wonder if they had reached Belichick through back channels.

Parcells: "I'm not answering that."

Gutman: "I just don't know, I just don't know."

Banks: "Well, [Belichick has] always been a step ahead, put it that way. There may have been some communications going on."

Henning: "Did he have a verbal deal? I don't know whether he had a verbal deal, but I know they had conversations. Things like that don't happen without having conversations. Let's not kid ourselves. This type of thing happens every day in our business."

Muir: "In retrospect, when I thought about it and put pieces to the puzzle together, I think there was a pre-arrangement between Kraft and Belichick. [Parcells] got wind of it and he knew if he retired or resigned, Belichick would be required by contract to be the head coach of the Jets.

"That explains [the] promptness of the resignation; it was to snare Belichick into the contract and screw Kraft. I do think Parcells was going to retire anyhow, but the promptness in which it was done was to try to get the rabbit in the snare trap."

Williams: "Belichick is one of the greatest ever. I knew it then. Everybody who was there knew it then. He's a genius at this game of football."

Jones: "It was like letting air out of a tire."

Green: "I don't want to say I felt betrayed because that's still his life, but I felt sadness because I felt like I was losing a mentor in Belichick. I always asked him questions about football. One time I asked him, 'How can I be better?' He said, 'First of all, I want you to move to the front of the meeting room.' From that moment, I sat in the front every single day. Even when he left, I always sat in the front of the class."

Banks: "I think Bill would've done a great job with the Jets and, yes, I think it would've changed the course of history."

Ramos: "Hindsight tells you it might have been the most important press conference in Jets history and New England history, based on the information that came from the press conference. Who knows what would've happened had Belichick taken over as head coach of the Jets? No one will ever know."

Tranchina: "I remember [Belichick's] very first Super Bowl with the Patriots. I said, 'I'm not watching it.' I went home to my one-bedroom apartment, drank a glass of wine -- a couple of glasses of wine -- and watched 'Sex and the City.' That was the first Super Bowl I didn't watch ... and then the second Super Bowl I didn't watch ... and the third ... Every one he was in, I couldn't watch it. I was so mad."

Gutman: "He's a successful coach, probably the most successful coach in the history of the league. I don't know what else to think of it. ... No [regrets]. You can't live that way, no."

Muir: "You have to give him credit. It took a lot of balls."

Parcells: "Obviously, I had a high regard for him. I'm happy he's done well. I'm the one who introduced him to the New England people (in 1996, when he hired Belichick as a Patriots assistant). I'm glad it worked out for him."

Jones: "He and [then Jets personnel executive] Scott Pioli and all those guys went up there to New England. I would see him at pregame and say, 'Why the f--- didn't you bring me with you?'" [Laughs]

Vinny Testaverde, Jets quarterback (1998-2003): "Years later, when I went to New England, toward the end of my career, a person whose name I won't reveal said someday we'll sit down, have a beer and talk about how the whole thing went down. To be honest, I never had an interest in knowing the story. Maybe some things are meant to be kept a secret."