In the letter, the elder Peterson questioned the fairness of the commissioners.
"When I gave Steve my guns there was no investigation to impede," Peterson said. "They were my favorite guns, and I was going to give them to Steve when I retired anyway. I only gave him three of the dozen or so guns I owned, and I kept most of my guns in my house and the police confiscated them all, so how could giving him those three guns impede anything?"
The board ruled the younger Peterson failed to disclose that his father gave him three guns and nearly $240,000, days after his father's 4th wife, Stacy, disappeared in October 2007.
Stephen Peterson was found not guilty of two other accusations by the commission. One related to his temporary possession of a sawed-off AR-15 assault rifle that his father used in connection with his duties as a Bolingbrook Police SWAT team member. The other accused Peterson of failing to keep the internal investigation into his possession of the guns confidential.
The former Bolingbrook police sergeant is not charged in Stacy's disappearance, but prosecutors believe he killed his third wife Savio in order to prevent her from testifying against him in court.
Her body was found in a dry bathtub on March 1, 2004.
Savio’s death was originally ruled an accidental drowning, but her body was exhumed after Peterson’s fourth wife, Stacy Peterson, disappeared on Oct. 29, 2007. A new autopsy reclassified Savio’s death as a homicide.
Stacy Peterson has long been presumed dead, but her body has never been found.