this is a long shot but... do you have the fic, I don't remember the name or the author sorry, dean is a cop and cas committed murder or something? but it wasn't actually him obviously. and they know each other years before the fic started. i'm so bad at this i'm so sorry
lmao as crazy as this sounds, I can actually think of two fics that were deleted that fit that description. There’s Lost Souls, Dean is a detective and Cas is his prime for suspect for murder, but he’s also his childhood best friend. And there’s Exonerated, Dean is the detective who put Cas in prison for murder but then years later he’s exonerated and Dean is the only link he still has from his old life. Is it one of those two? I’ve got both!