The hole in the fence

A person-sized hole appeared in the base's fence. Nobody saw it being made and everybody had seen it 'a while ago'. 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

• Álvaro, the youngest soldier: He's been at the base for two weeks. He's already worked out the fence is more decorative than anything.
• Branca, the base nurse: She treated a strange scratch on someone's hand the next morning.
• Cosme, the local shepherd: He walks his sheep along the fence every day. The sheep go through the hole too.
• Deonilde, the sergeant's wife: She lives in the next village and always knows first what's going on inside the base.