The French jihadist who killed a police couple at their home west of Paris had crossed paths with the policeman before, reports say.
Larossi Abballa is reported to have told negotiators: "He'd come to my house, now I have come to his."
After killing the couple, Abballa said in a video that he had acted on Islamic State orders.
Hundreds of colleagues and friends of the pair marched to their home on Thursday to pay tribute.
Police commander Jean-Baptiste Salvaing, 42, and his partner Jessica Schneider, 36, who worked at his police station, were stabbed to death in front of their three-year-old son on Monday night.
On Tuesday, French prosecutor Francois Molins said "Larossi Abballa knew Jean-Baptiste Salvaing was a policeman".
Mr Salvaing had been stationed in Mantes-la-Jolie, the town in which Abballa lives, before being moved to a different district.
But the information obtained by the newspaper Liberation from what it says are several police sources are the first indication that the killer and his victim may have crossed paths before.
On Wednesday the former girlfriend of Abballa spoke of his "isolation" after spending two-and-a-half years in jail.
The woman, who did not want to give her full name, told France Info radio the couple had dated for five years and remained close after they split up.
But after Abballa left jail last year, she said, he "preferred to keep his distance and changed friends".
In a video put out by a news agency linked to so-called Islamic State, Abballa was shown confessing to Monday's killings in the couple's home.
He said he was heeding a call by IS spokesman Abu Mohammed al-Adnani, who issued a message before the start of Ramadan inciting Muslims to target civilians in Europe and the US.
On Tuesday evening, President Francois Hollande said that the couple's three-year-old son and a child from Jean-Baptiste Salvaing's previous relationship would become wards of the state.
The status - which applies to children orphaned by acts of war, terrorism and in their parents' service to public security - means they will receive material assistance from the state as they grow up.
The couple's small son was at home when Abballa killed his parents. He was taken hostage for several hours, before Abballa was killed during the police assault.