Little Johnny goes to the police station

[rebbonk]

Little Johnny's kindergarten class was on a field trip to their local police station where they saw pictures tacked to a bulletin board of the 10 most wanted criminals.

One of the youngsters pointed to a picture and asked if it really was the photo of a wanted person.

'Yes,' said the policeman. 'The detectives want very badly to capture him.

Little Johnny asked,

Spoiler:

'Why didn't you keep him when you took his picture ?'