Mathieu got suspended from the team for smoking weed. He was brought back, at which point, he was suspended again... for smoking weed. Right before the season started, he was thrown off the team... for smoking weed. He made a huge deal out of staying at LSU, where he intended to play football again... until he got arrested... for smoking weed.
Weed related charges, four times in two years? Yeesh.
Even better - at least one of those cases involved 'synthetic' weed. Let's not draft the dude liable to bite someone's face off, eh?
If he could clean up his act, that would be one thing, but four offenses in two years is just ridiculous - especially the last one, when he absolutely needed to have his life straightened out.
He might go undrafted. At some point, he'd be worth the risk... but that's not until the 5th round or so, I'd bet.