Professor Peter Plum

Professor Plum has been jealous of Doctor Black since their school days together - Black stole Plum's only love from under his nose. Ever since he has been waiting to have his revenge.
Did the scholarly Professor unearth some dirt on his longstanding friend?
Here are some of the questions that Inspector Grey has asked Prof. Plum. Try to read as few as possible before making your guess (by clicking on the "Murder Cards" icon above).
Were you blackmailing Dr. Black?
What were you doing in the Library?
Why did you go to the Kitchen?
What did you do with the Spanner?
Was Reverend Green acting strangely tonight?