Rob Reiner and his wife Michele had their throats slit by a family member, possibly after an argument inside their Los Angeles home, leading to their tragic deaths … TMZ has learned

It’s unclear what exactly triggered the violence, which went down Sunday afternoon in Brentwood … but we’re told one of Rob’s daughters found her parents dead and told police a family member had killed them. PEOPLE reports the couple’s son, Nick, is being questioned in connection with the murders.

Our sources also say the daughter told police the family member “should be a suspect” because they’re “dangerous.”

TMZ broke the story … Rob and Michele suffered lacerations consistent with knife wounds, and LAPD’s Robbery Homicide Division is investigating the case.

Dispatch audio captures LAPD calling for backup to the Brentwood mansion around 3:30 PM … though it doesn’t provide any further information about the circumstances in the abode.

Rob was 78. Michele was 68.