Can a person with a criminal record get a visa to the USA?

Ok so my so fiance lives in Colombia. We want to get married 1. because we love each other and 2. because we will both have a better future here. The thing is he has a bad past. he went to prison for 9 months but it was only for an investigation. He's doing much better now and wants to put his life together and do things right. I was wondering though, even though that's in his record, can he still get a VISA to come to the USA. PLEASE HELP!