A hole the size of a person

The fence round the depots had a hole the size of a person. The report says rabbits made it. Big rabbits, the report admits. Some clues in this case come as riddles. If one stumps you, a hint will solve it. 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

• Aires, the sergeant on patrol: He patrolled every two hours. The patrol took ten minutes and the rest was rest.
• Bela, the corporal in charge of inventory: She counted the grenades three times. She got three different numbers, all official.
• Crisóstomo, the fence keeper: He's been patching the fence since 2015. He says the rabbits are getting more organised.
• Dina, the mess cook: She serves dinner at eight. That night there were second helpings and nobody did the patrol.