My aunt was shot and killed by her husband, please crime experts hear the evidence and give me your thoughts..

So they have a history of domestic abuse, he claims she was handing him a 9 mm gun and it accidentally went off and shoots directly through her temple, side to side. He has threatened to kill her numerous times. They were married over 20 years, and it made all the local news. We were all at the hospital when she died and the coroner sent her to the crime lab. Two days later the detective on the case told me they knew for sure she did not shoot herself. Yet didn't arrest him. He came to the funeral acting over the top distraught. Talked to the detective afterwards and asked him if he had an opinion about what happened. He tells me yes, but for the integrity of the case, he can't share and also doesn't want the family in an uproar bc he's waiting on additional crime scene and autopsy tests to be completed. Does this sound right?? Seems open and shut to me. Please crime experts weigh in!

A little background- in the months prior to her death he called certain family asking for dirt on her and even offered money..his control seemed to be unraveling. He has always had a drinking problem and was very violent, but he was not drinking the day of the shooting.