The Upper West Side family found butchered in a murder-suicide at their apartment this week all died from knife-induced neck wounds, according to the city medical examiner.

The conclusions support authorities’ working theory that Edison Lopez, 41, murdered longtime love Alexandra “Ola” Witek, 40, and the couple’s two boys, 3-year-old Lucian and 1-year-old Calvin, before slicing his own throat inside the West 86th Street home in which he was raised.