Were the cops going to shoot Mullen?

Agree with KDT. They were ordering Mullen to drop the weapon, because the purpose is to defuse/neutralize the situation, prevent any unnecessary violence. Unless one is a cop, or a federal agent, law enforcement officers will NEVER allow a person to shoot another person in their presence. Yes, they are aware Shaker is evil, and is responsible for the kidnapping of Mullen's son. They thought Mullen was intending to shoot Shaker because Mullen was pissed at him (as Mullen absolutely should be) for kidnapping his son and was trying to take the law into his own hands and seek revenge. They didn't know that Shaker was armed with another pistol on his ankle. Mullen did know, though. THat's why he picked up the weapon and pointed it at Shaker. He was merely using it as a precaution in case he needed to defend himself, not for revenge reasons. Mullen only fired, along with Agent Hawkins, when Shaker drew that second weapon. And the police started to arrest Tom, but Hawkins convinced them Tom was with them, the feds.