Both Jimi and Cosmo graduated from Holy Ghost Prep. I believe Cosmo was a year older than Jimi.
Jimi is the key to all of this IMO. 1st one to go missing and even though he went to school with CD they seemed to have 2 very different lifestyle. Jimi was all about sports and attending a prominent university. CD was all about guns, sneakers and ATVs and dropped out of college. Seems like DF and CD had a lot more in common.
Bingo.