Mantes-la-Jolie (France) (AFP) - Larossi Abballa, whose brutal stabbing of a French police couple was claimed by the Islamic State group, told friends of his "thirst for blood" as long as five years ago.
Abballa was convicted in September 2013 for belonging to a jihadist cell that recruited fighters to send to Pakistan.
Though his phones had been tapped since February as part of a probe into jihadists heading for Syria, Paris prosecutor Francois Molins said there was no evidence he was planning Monday's attack.
Hailing from Mantes-la-Jolie some 60 kilometres (35 miles) west of Paris, Abballa -- who wore his hair long but with a short beard -- had recently launched a halal sandwich company called Docteur Food.
But police had been aware of his desire to carry out attacks in France since his arrest in May 2011 when he was around 20.
At the time, police found an appointment book at his parents' home containing a list of police stations, mosques and tourist sites in his area, seen as potential targets for attack.
"Have to start the work. I'm thirsty for blood, as Allah is my witness," he had written to a friend, investigators say.
"He seemed very motivated by the idea of waging jihad," a fellow member of the cell told investigators, describing him as "bizarre" and "mysterious".
Previously known only for petty crime such as theft, he was arrested in 2011 on suspicion of having ties with Mohamed Niaz Abdul Rassed, an Indian national considered the instigator of the jihadist cell.
Text messages with other cell members left little doubt about his intentions, with one source close to the investigation saying he seemed "determined to commit violent acts in France".
"Do you really think they need us over there (in Pakistan)?" he asked his friend in 2011. "Allah... will give us the means to raise the flag here," he wrote.
- 'Kill infidels at home' -
Paris prosecutor Molins said Tuesday that Abballa told police negotiators before his death that he had sworn allegiance to IS three weeks earlier.
He told them he was responding to a call by IS leader Abu Bakr al-Baghdadi to "kill infidels, at home, with their families," Molins said.
He said police had found a hit list at the scene naming police and VIPS including journalists and rappers to be targeted.
In 2011, Abballa's phone, computer and a USB key were found to contain a raft of jihadist propaganda documents including videos and an Al-Qaeda brochure.
He and friends underwent religious and sports training north of Paris in the Val d'Oise department and the Seine-Saint-Denis suburb in late 2010 and early 2011.
Investigators say they even trained to kill rabbits by slitting their throats in a Val d'Oise wood.
Another revelation from his 2013 trial was that Abballa was to meet "brothers" from Belgium in December 2010.
The finding has all the greater resonance today given the links between the Paris attackers of November last year and those who targeted the Brussels airport and metro system in March.
- 'Intellectually limited' -
During his trial, Abballa seemed "intellectually limited... suggestible, not a decider," recalled defence lawyer Herve Denis.
He was convicted and sentenced to three years in prison, with six months suspended, but freed because he had served the time awaiting trial.
In January, Abballa launched the Docteur Food sandwich company, specialising in night-time deliveries, which he advertised on social media.
"He delivered sandwiches till late in the evening," said a neighbour in Mantes-la-Jolie, describing Abballa as "super nice".