As far as knowing more and speaking with the police goes.  It really doesn't matter what we tell the police because there's no way to prove that his cousin took the evidence from the scene. 

I can only tell you what I was told by two other individuals who spoke directly to him.  But that's only hearsay and won't help his case.  They won't come forward and talk 2 reasons 
1 They don't believe in snitching
2 they fear retaliation for speaking 

Hence why I said it's not what you know but sadly what you can prove in court. :(

As far as the commenters go.  I can only say it's not worth engaging most. They're pretty negative and unforgiving here.  It's not very productive.  So just focus on the case and what his lawyer is able to come up with.