PARIS — The killer who knifed to death two police officials in their home this week, claiming allegiance to the Islamic State, tracked the couple days before the murders and uploaded his claim of responsibility on the victims’ family computer, a judicial official said on Friday.

As the investigation into the gruesome deaths on Monday advanced, France honored the couple, Commander Jean-Baptiste Salvaing, No. 2 officer in Mureaux, a hardscrabble town west of Paris, and Jessica Schneider, a police administrator in nearby Mantes-la-Jolie, another challenging town for police.

Hundreds of officers convened for a somber ceremony at the prefecture of Versailles, the region where the two had lived and worked. President Francois Hollande, who presided, praised the couple as ‘‘two heroes of daily life.’’

Larossi Abballa, 25, convicted in 2013 for his role in a jihadi network, was killed by a police intervention unit that had surrounded the home and tried in vain to negotiate.

The couple’s 3-year-old son was found alive inside the home.

Signals from Abballa’s recently purchased telephone were captured in the town where the couple lived, Magnanville, and around the Mureaux police station on three consecutive days before the June 13 killings — on June 8, 9 and 10, the judicial official said.

‘‘One can imagine that [he] was tracking’’ Salvaing, said the official, who was not authorized to discuss the case publicly.

The investigation revealed yet another macabre aspect to the killings: Abballa uploaded his more than 12-minute video claiming responsibility — and pledge of allegiance to the Islamic State on Facebook Live — using the family computer.

It also appears he took photos of Salvaing from the family computer, the official said.

Associated Press