Original Roman (Wayne Northrop version) shot Orpheus' wife (accidentally - he thought she was a KGB agent), but we never saw it happen. We were told about it during the Stockholm/Treasury Bonds storyline.
In the flashbacks within that storyline, it was Drake Hogestyn's Roman who pulled the trigger. Since they shared the same memories, thanks to Stefano, they both believed they were the one that did it, but Orpheus isn't bothered with details like the face of the man that killed his wife, only that he wants revenge on John for having a happy life and on Marlena for, however she got into Stefano's hands which they didn't explain that either.
This explanation literally helps nothing and now my head hurts from typing this.