What do you do?

Walk up and place him under arrest. He might have a bomb. He might have a trigger for it, or he might have a dead-man's switch. It might detonate and kill you along with bystanders. That's a risk you take.

Unless you know with certainty that he has a bomb and does not have a dead man's switch, you don't just take his life because you're concerned about what-ifs.

It's no different than cops killing a man because he was holding a wallet, which they imagined might be a gun (e.g. Amadou Diallo).

Police need to stop pretending that they exist within fiction, where the outcome is known by the author. Just because you're afraid of something doesn't mean it's an actual threat.

Since 2001, there's been a real uptick in confusing fear and suspicion for evidence and knowledge.