It is obvious you know very little about family law.  A DV order does not accompany a complaint for divorce as a "Pro Forma Excercise".  It is not easy to get a DV order.  There has to be evidence.  There are, in fact, questions asked.  

The problem with this situation was not that he had a gun and had been charged with DV.  He did not seek to buy the gun after he was discovered to be mentally ill or after his DV issue.  He had the gun prior to that.  There is no legal provision for law enforcement to confiscate his weapon at that time.  A judge could have ordered it, but he flew to FL before further action could be taken.