Headscratchers / Den of Thieves

• After O'Brien acknowledges Donnie at the Benihana, Merrimen takes him back to the gang's hideout, accuses him of being a cop, and prepares to torture him. This would make sense if, as we're led to believe, Donnie was simply recruited as a getaway driver. But the ending reveals that Donnie was the one who masterminded the whole heist and recruited Merrimen to carry it out. So why would Merrimen ever suspect that Donnie is a cop?
  • Entrapment. At that point Merrimen probably suspects the whole thing might be a setup to catch his gang in the act of robbing a bank.
    • First of all, undercover cops specifically need to avoid entrapment. Merrimen would know that undercover cops could not actively recruit people for bank heists and then charge them with attempted robbery. Secondly, at this point, the gang has already murdered multiple law enforcement officers while stealing the armored car. How could Merrimen think that Donnie is an undercover cop when Donnie hasn't already arrested them all on multiple first-degree murder charges?
    • Merrimen clearly knows that he's not dealing with normal cops, but with some dirty people using very underhanded tactics. Better to be safe than sorry. Merrimen can also just not know all details of police procedure and so he's unwilling to take the risks.
      • Even if Merrimen somehow managed to convince himself that Donnie had masterminded the perfect robbery just to trick a couple crooks into committing the robbery so he can arrest them, that still wouldn't explain why Donnie hadn't struck the moment after he watched Merrimen commit quadruple cop murder.
• The police officers killed at the opening donut shop shootout look like city cops, but the crime scene is investigated by O'Brien and his Sheriff's deputies, so is the donut shop in city jurisdiction or county?