An unsolved football mystery is back in the news. And the man who put it there is the man who caused it in the first place: Bill Belichick. We refer, of course, to the Case of the Disappearing Cornerback from Super Bowl LII.

The incident took place on February 4, 2018, in the U.S. Bank Stadium in Minneapolis, Minnesota, the northernmost city to play host to a Super Bowl game. It was the Super Bowl game between the New England Patriots and the Philadelphia Eagles. The Patriots had been installed as five-point favorites because the Eagles starting quarterback, Carson Wentz, was out with an injury. He would be replaced by his backup, Nick Foles. The big surprise of the night was that when the Patriots defensive unit took the field, their starting cornerback, Malcolm Butler, was nowhere to be seen. Oh, you could see him if you looked over to the New England sideline, but he wasn't in the game, and he wouldn't be, except for one punting play.

Foles, the substitute Eagles quarterback, took advantage of an especially porous New England secondary by playing the game of his life, completing 28 passes in 43 attempts for 373 yards and three touchdowns. He also caught a pass for a touchdown and Philadelphia won its first ever Super Bowl, 41 to 33. Foles was the game's MVP.

Tom Brady, despite being on the losing side, was hardly outplayed by Foles. He threw for 505 yards, a postseason record, and wracked up three touchdown passes of his own. In fact, he brought the Patriots back from a 10-point half-time deficit and had them in the lead, 33 to 32, with 9:22 left on the clock, but their leaky defense could not stem the tide. The Patriots' 33 points were the most ever scored by a losing team in Super Bowl history. Brady's quarterback rating for the game was 115.2 as opposed to Foles's 106.1. Tom didn't get to go to Disney World but he covered himself with glory that night and cemented his reputation as the Greatest of All Time.

Through it all, Butler, who had started 15 of 16 games that season, was relegated to the sideline, save for that one punting play. Surely, he could have made a difference just as he famously had three years earlier in Super Bowl XLIX when, with just 20 seconds remaining in the game, he stepped in front of Seattle Seahawks wide receiver Ricardo Lockette to intercept a pass, preventing what seemed like a sure Seattle touchdown and saving the game for the Patriots, 28 to 24. It was one of the most famous plays in Super Bowl history.

What had happened this time? Why had Belichick totally "ghosted" his starting cornerback in the biggest game, played before the biggest audience of the year? It arguably cost the Patriots the game and the championship. The coach, who is notorious for being stingy with information he doesn't want us to have, simply said when it was over, "Coach's decision," and left it at that. For his part, a puzzled Butler would say, "I don't know what it was. I guess I wasn't playing good or they didn't feel comfortable. I don't know. But I could have changed that game." Even owner Robert Kraft had reportedly been taken by surprise by Butler's benching. So we were left to just speculate as to the reason for it. Was it a disciplinary measure? Had Butler broken any team rules? Had he had any run-ins with any of the coaches? Was he a bad teammate? Whatever it was, it must have been pretty egregious for Belichick to risk a championship.

That March, Butler, a restricted free agent, signed on with the Tennessee Titans, for whom he was the regular cornerback for the next three seasons. In the spring of 2021, he inked a deal with the Arizona Cardinals, but announced his retirement before the season started. This past winter, the Cardinals granted him his release, making him eligible to sign with any team.

It was then he announced that he was going to try a comeback, and the first team to invite him to tryout was, you guessed it, the New England Patriots. They signed him up, thereby guaranteeing that all the unanswered questions from Super Bowl LII are going to be asked all over again.

If Belichick didn't think Butler was good enough to play even a single down on defense four years ago when the chips were all on the table, what makes him think that he is now, at age 32 and after a full season in retirement? Have the Patriots regressed from their glory years to the point where a player who was callously tossed aside back then is viewed as a valued asset now? What really happened on that February Sunday in 2018, and, more important, why?

Inquiring minds and frustrated Pats fans want to know.

- Dick Flavin is a New York Times bestselling author; the Boston Red Sox "Poet Laureate" and The Pilot's recently minted Sports' columnist.