As a result of Ducky's testimony, Vincent was found guilty and sentenced to eight years in jail for the crime with his sentence wearing heavily on Mary who held a strong yet clearly insane belief that her son was completely innocent of the crime despite all the damning evidence that portrayed Vincent as the killer.
This caused her to develop a bitter resentment and grudge against all local enforcement personnel and NCIS Agents.
When Vincent got out, he was bitter and sought revenge against those who had ruined his life which also prompted him to begin drinking rather heavily.
He and his brother Jonathan were driving one night and they hit a tree with both siblings managing to get to safety although the Hanlans later used a body taken from the funeral home and lied to the authorities, informing them that Vincent had actually perished in the crash when in reality, he had survived and was still alive.
At some point, Mary began aiding her son in capturing the people who had overseen Vincent's trial. They later killed the victims by presumably draining them of their blood before cutting up the corpses and dumping them in barrels dosed with alcohol which they later dumped behind Bethesda Naval Hospital, putting the case into NCIS jurisdiction and into the hands of Ducky who had since become the NCIS Medical Examiner.
A year or so later, Ducky realized that one of the bodies was an attorney he once knew and that the meat puzzle bodies were connected to the Vincent Hanlan case, forcing NCIS Special Agent Leroy Jethro Gibbs and his team to reopen the case as they attempted to capture the killers while Ducky was put into protective custody.
The team, racing against the clock to find Ducky, dragged Vincent's brother, Jonathan back in for questioning where Gibbs spent hours interrogating him as his team looked on.
In the meantime, Palmer and Forensic Scientist Abigail Sciuto uncovered a shocking truth that everyone had missed: the body that was originally thought to have been that of Vincent Hanlan was in fact someone else altogether and that the teeth in the corpse had been removed from Hanlan's mouth and placed in the body.
Jonathan eventually broke down and gave up the location: the Funeral Home. At night-time, Gibbs and the team waited until the Hanlans had gotten Ducky out of his hiding place and stormed the funeral home, using stealth tactics. They were successful in saving Ducky who was just seconds from having his blood drained.
Unable to face the possibility with going back to prison, Vincent committed suicide, leaving Mary devastated and grief-stricken while screaming that NCIS had killed her son.
Her final fate is not known but it's presumed that she received a very long sentence for aiding and abetting her son in his revenge-killings.