Changing my theory here.
I could be wrong, but this is looking more and more like RC had an obsession for Annie Le. She was most likely cordial to him as an employee of the lab, and he took it to be more than that or hoped it would be more than that. I could see him foisting himself on her. Her rejecting him, and him then deciding to strangle her. Maybe he even built those biceps up for her. I'm sure we'll find out all about it in the weeks to come.
At first I took him to be just mentally unstable, but with what I've been reading from people who knew him and a relative, it's looking to be more sinister. Stories about him from fellow classmates differ. Some thought he was a good guy, other's weren't even shocked when they heard the news. RC's own cousin said he had anger management problems as a child.
One poster from RC's high school said it's erroneous that he was in the Asian Awareness Club. Said RC just showed up & got in the group picture the day they were taking photos.
People say he was an athlete, but he was only a member of each sport's team for one year. A coach didn't even remember the guy as being an athlete. I hate to be making references to a media source's commentaries, but that's where I got the info, and I don't even remember which one.