The envelope with no sender

Three weeks later, some of the documents came back to Parliament in an envelope with no sender, too many stamps and one sheet missing. Some clues in this case come as riddles. If one stumps you, a hint will solve it. Not every row and column has to be occupied.

Suspects

• Albertina, the internal post clerk: She weighs every envelope. This one weighed less than it should, and she made a note.
• Benício, the MP who got the envelope: He opened the envelope live on camera. One sheet was missing, and it was the only one he cared about.
• Cidália, the stamp expert: She says the stamps come from a 1987 collection. The sender has good taste.
• Dâmaso, the courier: He delivered the envelope without asking for a signature. He says it looked urgent.