>> so I wasnt responsible  <<

Um.... incorrect.

In addition to Mike-In-MD's correct answer, read this ... carefully!
http://www.fdic.gov/consumers/consumer/news/cnwin0607/scams.html

Extract:
"In these cases, the depositor most likely will be held responsible for the entire amount of the fraudulent check."

Instead of cashing the check, or sending it back, take it and the envelope in which it came to the post office.  They will use it as evidence and pursue the scammer.