Police say the man lay in wait outside the policeman's house before the ambush took place at around 20:30 (18:30 GMT). After the murder he went inside the house and killed the policeman's wife, and held their three-year-old son hostage.
Abballa, 25, was shot and killed when police entered the couple's home in Magnanville at about midnight, hours after he posted a 13-minute video on Facebook Live in which he swore allegiance to IS.
In the video, he was shown considering what to do with their son, according to French jihad expert David Thomson, who watched it.
"I don't know yet what I'm going to do with him," the killer is heard saying.
Larossi Abballa stabbed Salvaing, 42, a deputy police commander, then slit the throat of Schneider, 36, a police administrator, in front of the couple’s three-year-old son.