The son of former Virginia Lt. Governor Justin Fairfax called 911 after Justin allegedly shot his wife and then himself ... and we have the harrowing dispatch audio.

According to the audio, the incident was initially called in as a stabbing. The dispatcher is heard saying that Justin's wife, Cerina, is lying on the ground with holes in her shirt.

The son didn't immediately know where his dad was, according to the audio, but saw that his car was still there.

Later, an emergency responder tells the dispatcher he's found Justin, 47, at the home with no pulse, referring to him as an "obvious D.O.A."

Police tell TMZ, cameras inside the home corroborate the account of a murder-suicide. We're told Justin shot his wife dead before turning the gun on himself. Fairfax County Police told TMZ ... Cerina's body was found in the basement and Justin's in the bedroom.

Justin and Cerina wed in 2006 but were reportedly going through a "complicated" divorce. They had two children -- both of whom were reportedly home at the time of the incident.

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