The patrol that never happened

The base had patrols scheduled every hour. In the logbook they were all signed off. In the fence there was a hole nobody signed for. Four people and one grenade: one person per row, one per column. Whoever is left alone with it in the same room is the one you're looking for.

Suspects

• Abel, the night shift sentry: He should have patrolled every hour. He did one, at midnight, and thought that was enough.
• Brenda, the corporal on duty: She signs the patrol log. She signed the whole thing at once, for efficiency.
• Cipriano, the depot sergeant: He has the key to the depot and the conviction that nobody else does.
• Dora, the jeep driver: She drove past the fence three times that night. She says she was testing the brakes.