No. Not all insiders would necessarily be professionals as covering their tracks post crypto hack. They could just be someone who knew they had access to the keys and said "screw it my life is already horrible lets try this".
Another option is honestly an insider who got screwed (a lot of employees had a TONNE of money on FTX) selling the keys they knew of to someone else.
Or they got screwed and thought about how to screw the higher ups even more. They never need to cash out the money to do this.
Nobody will ever not be suspicious of SBF and his inner circle again after this hack.
If it were just a big collapse and it went like an ordinary bankruptcy with the creditors getting a haircut, he'd just be considered an idiot. Money mysteriously vanished? Now he's malicious as well, and any court is going to ask SBF where it went, and even if he didn't know nobody would believe it.
The latter immediately occured to me. It is a lot easier to claim ignorance if your key gets used by someone else to drain the vault, than it is to drain the vault yourself.
Another option is honestly an insider who got screwed (a lot of employees had a TONNE of money on FTX) selling the keys they knew of to someone else.