Best I can remember, he spent his final year of high school with extended family in Aurora, CO. Word was that there were a lot of bad influences back in Oakland he wanted/needed to get away from.
A 2010 class recruit, he was then going to attend Notre Dame, but after the coaching change there he opened things up and was convinced by Cal that he should come back home for college (despite a lot of negative comments he'd previously made about Cal and going back).
He did not adjust well with being back in the Oakland area and realized it was a mistake. Not sure what all was going on, but when he decided to transfer to Florida in July 2010 (after signing with Cal in February 2010)
he was quoted as saying, "I would like to thank everyone who has been supportive of me through my crazy mental episodes. A special thank you to my mother and father who have supported me no matter what. I love you both. God has granted me a second chance. A chance I cannot mess up. With that said. Go Gators. Thank You to everyone and all the coaches who showed their interest in me."
He redshirted at Florida under NCAA transfer rules, then was charged by police in January with misdemeanor marijuana possession. He's under a deferred prosecution agreement, so he needs to avoid another run-in with the law or that will come back to bite him. The reasons given for the transfer from Florida, according to Coach Muschamp, are that his family wanted him closer to home.
Talent-wise, they thought very highly of him in Florida. They were expecting him to be a playmaker as a RS-Freshman as an edge rusher.
CU would have to gauge whether "closer to family" could mean back in Colorado where he didn't have any personal problems. But he did complain a bit about the weather (which made his initial verbal to Notre Dame a surprise to a lot of us who follow recruiting closely). If he'd like to come here, the coaches would have to decide whether he's a good fit for the culture being built. I don't think the talent's in question.
Here's a recent photo of Martin (I think from the spring game):