An official in France has said there is a “strong body of evidence” to suggest Frenchman Medhi Nemmouche shot dead three people in an attack at the Jewish Museum in Brussels.

A fourth victim, believed to be an employee of the museum, was critically injured in the attack.

Paris prosecutor François Molins told a news conference the 29-year-old is being held on charges of murder, attempted murder and possession of weapons, all within the framework of terrorist activity.

According to Molins, the suspect made a film about the attack.

“We do not see the cameraman in the film, but his voice can be heard and it appears to be that of Mehdi Nemmouche,” said the prosecutor. “And he explains that this video was made because a live recording of the shooting in the Jewish Museum by the GoPro camera didn’t work.”

He added that Nemmouche became radicalised during several stays in jail in France, then spent a year in Syria.

“He spent over a year in Syria, where he seems to have joined the ranks of combatant groups, jihadist terrorist groups,” he said, adding “During his last stay in jail he was noticed for extremist (Islamic) proselytism. On December 31 2012, three weeks after he was freed, he travelled to Syria.”

French President François Hollande also spoke to press.

“We have to ensure these Jihadists, of which there are around 700 in our country, who have already been, or are still over there, can be followed and be prevented from causing disturbances where they are. Namely upon their return to France or Europe.”

When arrested in Marseille on Friday, Nemmouche was reportedly in possession of a Kalashnikov assault rifle – similar to the weapon used in the attack – and another gun.

His clothes are said to be similar to those worn by the shooter.

According to Molins, he has not yet said anything.

Belgium, meanwhile, remains in a state of high alert, according to its federal prosecutor.