I highly highly recommend against doing this!!!! By doing a password recovery you are on the hook for any illegitimate content that the person might have uploaded/shared and might get you in real legal trouble. Instead I recommend filing a complaint without claiming the account.
No, you aren't. Certainly someone might try to claim that it had been you. Worst case I suppose you could actually end up in court but that's true for pretty much any accusation.
I doubt it would be an issue in practice though. Far more likely is that you might inadvertently get caught up in a ban from the service due to the illicit content being linked to the account you recovered which would now be linked back to your metadata (IP address & etc) since you recovered it which would in turn link to your regular account.
