The visitors' book

In Parliament's visitors' book, the first signature of the day is always the same clerk's. That day there was a signature before his. Four people and one piece of evidence: 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

• Afonso, the receptionist: He records who comes in in a green-covered book. Who goes out, he records from memory.
• Benilde, the early-bird MP: She always arrives before everyone else. That day she arrived even earlier.
• Celso, the parliamentary group's driver: He waits in the garage and comes up for coffee. He comes up a lot.
• Doroteia, the intern: She's doing an internship on transparency. She picked the right week.