I was looking for the meaning of informer in Oxford Learnear's Dictionary. I got the meaning but the first example sentenses is not understandable to me.
Here is the complete definition and example sentences as in the dictionary (my question is related to the highlighted sentence):
informer
a person who gives information to the police or other authority.
The bomber turned (= became) police informer to escape prison.
One of the gang members had turned informer.
The meaning of the verb turn is my problem. If "turn" means "become" as the dictionary has written in paranthesis, what is the role of escape? Who has escaped from the prison? The bomber or the informer?
Please explain a little about the structure of the sentence. For example, what is the role of "to" in "to escape prison"?