An Albanian couple was arrested Sunday in connection with last week’s truck attack that left 84 people dead in the southern French city of Nice. The couple is suspected of supplying 7.65 mm automatic pistol to Mohamed Lahouaiej Bouhlel, the truck driver who rammed his vehicle into people celebrating Bastille Day in the city.

According to French authorities, it is the same pistol Bouhlel used to fire at police before they fatally shot him. A total of seven people are in police custody in relation with the attack claimed by the Islamic state group, also known as ISIS. Bouhlel was a Nice resident with dual French-Tunisian citizenship.

French police had arrested Bouhlel’s estranged wife Hajer Khalfallah Friday. She was released Sunday morning without charge. The 31-year-old was abusive with Khalfallah during their marriage following which they split. Her lawyer Jean-Yves Garino said the mother of three has not been in contact with Bouhlel for a while. Reports indicated that Bouhlel became depressed after Khalfallah divorced him.

Meanwhile, French media reported that data from Bouhlel’s mobile phone — picked up by officers after he was shot dead — showed he used dating websites and experimented with drugs and drinks. According to his brother, Jabeur Bouhlel, the attacker had called him hours before the killings and sent a selfie taken during the Bastille Day celebrations.

“That last day he said he was in Nice with his European friends to celebrate the national holiday,” Jabeur said, according to Sky News. He added that in the picture “he [Bouhlel] seemed very happy and pleased, he was laughing a lot.”

ISIS had issued a statement Saturday saying that Bouhlel was one of the “soldiers of Islam” and he “carried out the operation in response to calls to target nationals of states that are part of the coalition fighting Islamic State.”

However, some experts are of the opinion that that ISIS’ claim does not necessarily establish a direct link between the attack and Islamic extremism.

“Islamic State called for such [individual] attacks to be carried out back in 2014. They are also using the public perception that an attack like this seems to fit Islamic State,” Edwin Bakker, a professor at the Centre for Terrorism and Counterterrorism at the University of Leiden in the Netherlands, told Reuters. “Investigators still have not discovered a direct link between Islamic State and the attacker, so it is a cheap claim.”

A few years ago, psychiatrist Chamseddine Hamouda conducted Bouhlel’s mental assessment after his father became concerned about his “troubling behavior of a psychotic nature.”

“He was a stranger to himself,” Hamouda told BBC, “I advised his parents that he needed treatment.”

“At the time he exhibited violent behavior towards his family, but one cannot imagine that a person like that could carry out such a horrific and bloody crime on this scale. I’m sure that in the past 12 years something else happened that perhaps influenced how he thought,” Hamouda added.

Bouhlel was known to police for petty crimes and he was given a suspended six-month prison sentence this year after being found guilty of violence with a weapon. He, however, was not on terror watch list.