CHICAGO (AP) - A Northwestern University professor and journalism students who spent three years trying to show the wrong man was convicted in the 1978 killing of a security guard may now have to defend themselves.

Cook County prosecutors have issued subpoenas to professor David
Protess for his students' grades, his syllabus and their e-mails. Prosecutors claim the students may have been under pressure to prove the case to get a good grade.

Protess and his investigative reporting students have helped free 11 innocent men from prison, including death row, since 1996.

But Protess says in two other cases students found compelling evidence of prisoners' guilt and received As. He says students are rewarded for finding the truth, not getting convictions overturned.