From football matches to international jihad, the 25-year-old Frenchman David Drugeon converted as a teen to Islam and drifted toward ever more radical groups, up until his death in July in a coalition air strike in Syria.

Drugeon -- by now a bombmaker for an Al-Qaeda offshoot -- was believed killed once before, in an airstrike in November 2014. This time his death has been established beyond doubt by US officials.

Born in 1989 into a middle class family in the Brittany town of Vannes, he became passionate about football and would travel to the southern city of Marseille with his father to see his favorite team, OM, play.

When his parents divorced in 2002, Drugeon and his brother Cyril drew close to ultraconservative Salafist Muslims who would gather in their neighborhood.

The two brothers quickly converted to Islam and David -- who was just 13 at the time -- became known as "Daoud," started learning Arabic and studied the Koran.

On his page on "Copains d'avant," a Facebook-style French website, he is seen posing in a white shirt, unsmiling.

On the list of countries he "dreams of visiting," he wrote: "Afghanistan, Algeria, Saudi Arabia, Ethiopia, Iraq, Israel, Morocco, Pakistan, Somalia, Sudan, Syria."

- Explosives expert -

"He was a sweet guy who didn't cause any trouble. A football enthusiast," a former classmate in Vannes who wished to remain anonymous told AFP.

A woman whose daughter was in his class added: "His father was a bus driver. The boy studied hard. We don't understand what went through his head."

After having worked and saved money, Drugeon eventually went to Egypt and studied in religious schools where he deepened his knowledge of the Koran and of Arabic.

He returned to France, but at the start of 2010 told his family he was going back to Egypt. In reality, like many before him, he went down the jihad route and traveled to tribal zones in Pakistan.

There he met a Belgian man of Tunisian origin, jihad veteran Moez Garsallaoui who was considered an important member of Al-Qaeda in Europe and then in the Pakistan-Afghanistan region.

He taught "Daoud" how to handle explosives and make bombs.

A security source, who asked not to be identified, said he became a "relatively good" explosives expert.

- Children make 'easy prey' -

According to a senior French official, Drugeon never belonged either to the French military or intelligence services, as some reports had suggested.

"He is well known to our intelligence services and those of the United States, he is quite important in his organization, with some technical knowledge. But you don't learn to handle bombs in the French army."

As the conflict in Syria progressed and the country became a "land of jihad," Drugeon -- like many middle-ranking Al-Qaeda operatives fed up of constantly living under the threat of US drones and their missiles -- left the Pakistan-Afghanistan area and set up shop in Idlib.

Drugeon, who went by the nom de guerre Hamza al-Faransi, was described as a key figure in the Al-Qaeda offshoot Khorasan group, which operates in Syria and which American officials say is a dangerous militant outfit planning to attack the United States and other Western countries.

His father Patrice Drugeon said he had chosen to die as a "martyr."

"That's what hurts me the most. What he became. What he was made to become, the indoctrination," he told AFP in a phone interview.

"We have to watch out for our children, and for all those young adults who are at a loose end these days. They make easy prey" for jihadist recruiters.

"I think of my son every day. I have his picture here before me. If he is indeed dead, may his soul rest in peace."