To prove the volatile temper that got him kicked off his college team had been tempered by time.
To prove the Chiefs were not foolish to spend such a high pick on him.
To prove he can be one of the best defensive backs in the league.
So far, he's been able to prove each of them.
After his second pick-6 of the season on Sunday in Baltimore, Peters has firmly placed himself in the defensive rookie of the year race. He was just voted to the Pro Bowl, and was the AFC defensive player of the week after helping Kansas City to its eighth straight victory.
''He's had a great year, there's no question,'' Chiefs quarterback Alex Smith said. ''I don't know how many turnovers he's generated, but they're huge. He battles all the time, and his attitude seems to have spread throughout the team. It's very rare for a young guy to have such a great attitude.''
He also has 23 passes defended, and one of those ricocheted to linebacker Derrick Johnson for another interception. Throw in the fumble that Peters forced and he is responsible for at least nine turnovers this season.
To put that into perspective, three teams have managed fewer interceptions than Peters, and two more are tied with him. He's had more touchdown returns than all but six defenses in the league.
Those nine takeaways? It's the same number Dallas has produced.
Peters has done it all with youthful exuberance bordering on flamboyance. Case in point was his 90-yard TD return against the Ravens, which he celebrated by breaking into Ray Lewis's celebratory dance.
It was homage to the retired Pro Bowl linebacker, Peters said, and not a slight.
''Playing in his house - he was here for a long time, and he did a very good job. So that's an honor and salute to Ray Lewis,'' Peters said. ''I knew if I got a pick I was going to do it.''
That play and celebration capture perfectly the Chiefs cornerback.
His talent has never been in question, all the way back to his days leading McClymond's to its first perfect season as a high school senior in Oakland, California. After a redshirt season at Washington, his talent allowed him to become one of the best defensive backs in the Pac-12.
But a coaching change didn't sit well with him, and Peters got into several arguments with new boss Chris Peterson. He was ultimately kicked off the Huskies team during his senior season.
At that point, his story could have gone two ways: He could have continued a spiral and his career could have been finished, or he could have taken the difficult road of atonement.
He did the latter.
Peters made amends with Peterson, who did not allow him back on the team but at least allowed him the use of Washington's workout facilities. He became a model citizen off the field, maturing even more rapidly once his newborn arrived, and impressed most NFL teams when he discussed all the issues that he had at Washington during the NFL's scouting combine.
The Chiefs were among the teams that talked to him. Still, they decided to send personnel to spend time with Peters in Oakland shortly before the draft, just to be certain of his character.
''It's the way he carries himself, the way he goes about his work,'' Chiefs coach Andy Reid said. ''We're not a big hazing team and all of those things anyway with rookies. We expect them to come in and play and produce.
''And so that's what I think they see, a kid whose dad was a coach and he grew up around it and has a pretty good feeling for the game, and then he's making plays on the field.''
Now, with the Chiefs (9-5) in playoff position heading into their final two games - at home against Cleveland and Oakland - Peters is putting the finishing touches on a memorable rookie season.
''Rookies at about this time in the year, they're kind of working through that wall, that rookie wall where their season's over and they're resting up for bowl games,'' Reid said. ''He's pushing through that and doing a good job with it. He's a competitive kid - he's having a good year.''
NOTES: Pro Bowl LB Tamba Hali had three small screws inserted to repair his broken right thumb, though trainer Rick Burkholder said he could play Sunday against Cleveland. ... WR De'Anthony Thomas was expected to practice after missing three games with a concussion.
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