I think it was Edna. She had the motive and no-one saw her during the wedding. She's playing it really cool, pretending she didn't even know he was dead. Go Edna!
Edna is not one of the 10 possible murderers given, so can't be her. The only one's it can be are Jimmy, Matthew, Carl, Bob, Terry, Jamie, Len, Grayson, Rosemary or Chas. I reckon one of the last four - Len or Grayson in particular.