The comments

Under the video there were thousands of opinions about pitch, written by people who have never tuned anything. Some were jokes, others weren't any more. The phone where the worst ones were read was forgotten at a social club. Four people and a phone: 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

• Acácio, the brass band conductor: He read every comment and corrected the pitch of each one. He gave up after two hundred.
• Brites, the club president: She posted a comment asking for respect. It got three likes, all from family.
• Cornélio, the bass drummer: He doesn't read comments. He says nobody notices whether a bass drum is in tune.
• Dina, the treasurer: She counted the comments the way she counts membership fees: one by one, pencil behind her ear.