Cameras under maintenance

The base's cameras had been broken for two years. Parts were ordered, forms were filled in and the parts arrived the day after the theft. Some clues in this case come as riddles. 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

• Agostinho, the camera technician: He ordered parts for the cameras two years ago. The parts arrived the day after the theft.
• Benjamim, the sentry: He spent his whole watch looking at the camera screen. The screen was off, but very calming.
• Custódia, the equipment sergeant: She counts the grenades every Friday. That Friday she counted twice and got the same wrong number.
• Delfim, the maintenance corporal: He fixes everything except what he's asked to. He was asked to fix the cameras.