One snowy night, Sherlock Holmes was in his house sitting by a fire. All of a sudden a snowball came crashing through his window, breaking it.

Holmes got up and looked out the window just in time to see three neighborhood kids who were brothers run around a corner. Their names were John Crimson, Mark Crimson and Paul Crimson.
The next day Holmes got a note on his door that read "? Crimson. He broke your window."
Which of the three Crimson brothers should Sherlock Holmes question about the incident?

Holmes should question Paul Crimson because the note left on his door only had a question mark and the last name "Crimson." Since there is no specific name mentioned, Holmes should question all three brothers to gather more information about the incident.