Only one of the two suspects could have seen what he said he’d seen.

If you guessed it had something to do with the stain being on the way TO the crime scene, then you fell for a red stained herring.

Nobody said the stain was blood. It could have been tomato sauce from the hotdog. It really doesn’t matter because Alfonso made it up…

Let’s go back to the office – from the front door you enter the atrium with the cafeteria. Straight ahead is the passage to Callan’s office. To the left is the passage to Dean’s office and to the right is the passage to Alfonso’s office.

If Alfonso had seen Callan walking to Dean’s office like he said, Callan would have been walking away from Alfonso. Alfonso would have seen Callan’s back and could not possibly have seen his shirt pocket. He made up his story.

Callan’s office was down the centre passage. Alfonso would have had to walk past on his way through the atrium to Dean’s office.

Callan’s story is possible. Alfonso’s story is impossible… and we had him!