A man accused of decapitating his mom, dad and their dog in Southern California had a strange reaction to being shot ... belting out Tina Turner while lying prone in the street.
Joseph Gerdvil -- arrested on two counts of homicide in San Juan Capistrano -- allegedly appears in new body cam footage ... coming face to face with cops on a street outside San Juan Mobile Estates.
Check out the clip ... an officer jumps out of the car and draws his weapon -- telling the man approaching him, which police say is Gerdvil, to stop moving.
When the individual keeps coming, the officers fires multiple shots, taking him down.
Later on, cops are standing over the man's body ... and, after telling them to finish him off with a shot to the head, he begins to sing.
He sings out a couple lines from Tina Turner's hit song "What's Love Got to Do With It?' ... crooning, "What's love got to do, got to do with it? What's love but a second-hand emotion?"
Gerdvil stands accused of killing both his parents -- 79-year-old Antoinette and 77-year-old Ronald -- and their pet chihuahua back in early July.
According to the Sheriff's Department, officers arrived after receiving a call about a blood soaked man chasing a mainteance worker at around 7:40 AM ... which is when this shooting went down. Gerdvil was taken to the hospital.