Don Sanderson was convicted of killing his wife and daughter and sentenced to life in prison 25 years prior.
Since then, he has maintained his innocence while acting as the model inmate.
Morgan, who has been monitoring Don for years, recommends him for parole and the board agrees. Don is set free.
After less than three days of freedom, however, Don is caught at the scene of another killing: DC bachelor Tom Wittman.
Don pleads that it was self-defense - he knows that Tom was there the night of his family's murder with two other assailants and he needs to find the real killer.
The BAU takes the case and begins the search.
Through Tom's belongings, Morgan uncovers the second assailant: a local woman named Mary Rutka.
The BAU storms her house, but find her dead on the floor as a hooded man flees out the back. Since Mary dies without revealing the truth, the trail seems to have run cold.
Prentiss and Morgan, profiling the UnSub as a psychopath, determine that there's only one reason Mary would have survived for so long: blackmail.
She must have had evidence of the crime that would implicate the still-unknown ringleader.
After a search, the uncover an old videotape from the night of the killing with the voice of the UnSub on it.
Prentiss recognizes one of the things the UnSub says as the slogan for politician James Anderson, a particularly ruthless figure on the hill. His persona matches their profile perfectly, so they move in.
In the end, Garcia is able to match Anderson's voice with the voice on the tape, and the BAU uncovers the dirty politician as the killer.
Don is finally vindicated and united with the son he hasn't seen in 25 years.