HELP i am so scare i was applying on-line looking for jobs and in newspaper. I got a check in the mail?

i called the numberon the letter and the bank number on the check and they said that it was a valid check. I went to go and cash it and they called the police on me and said that i was trying to cash a fraudelent check. I swear i did not know that the check was fraudelent. I called and what i thought i was doing was trying to make sure that it was not a scam but i guess it was. The police came and they was asking me all of these questions telling me that i was lying. I told them exactly what happen and i also gave them the letter that came with the check. They said that the prosecutor is going to have to look into it. What can happen to me? Will I go to jail? I do have a record a theft in 2001 and a atttempted felonious ault(not as bad as it sound)but i had never commited or tried to commit fraud. Thank you to all that answer without being rude or ignorant everybody makes mistakes. The check was for a high amount. Has this ever happen to anybody and if so what happen to you?