Former Virginia Lt. Gov. Justin Fairfax's Wife Set Up Cameras in Their Home

Former Virginia Lt. Gov. Justin Fairfax's wife, Cerina Fairfax, evidently felt the need to beef up the amount of security measures taken inside their house before Thursday's apparent murder-suicide ... she set up a bunch of cameras in the home.

As you know ... police believe Justin shot Cerina dead early Thursday before turning the gun on himself. The couple was reportedly going through a messy divorce ... during which Cerina had the cameras installed, according to cops.

Fairfax County Police Chief Kevin Davis told reporters outside the family's Annandale, VA home Thursday that they first became aware of the cameras in January when they were used to discredit Justin's claims that Cerina assaulted him.

Now, those same cameras have been used to corroborate the details of Thursday's shooting.

The couple was separated but living together, according to the documents we obtained, which police also confirmed today.

Chief Davis said, "I know he was served some paperwork recently. Apparently, the paperwork indicated when he was next to appear in court. That may have been a spark and detectives will figure that out that that led to this tragedy here."

Justin and Cerina shared two kids -- Cameron, born in 2009, and Carys, born in 2011 -- both of whom were reportedly at home during the grisly killings.