PARIS (AP) — Former French President François Hollande told a special terrorism court on Monday that the man who drove a truck into a crowded beachfront in Nice on Bastille Day six years ago, killing 86 people, was a terrorist who had gone undetected by security services despite France being on high alert for extremist attacks following the Islamic State massacres in Paris.

Thousands of people had packed Nice’s famed boardwalk on the Mediterranean coast on July 14, 2016, to celebrate France’s national holiday. Shortly after the end of a fireworks display, the truck careered through the crowd for two kilometers (1¼ miles) like a snowplow, slamming into person after person. The final death toll was 86, including 15 children and adolescents, while 450 others were injured.

The attacker, Mohamed Lahouaiej Bouhlel, a 31-year-old Tunisian with French residency, was killed by police soon afterward.

The Islamic State group claimed responsibility for the carnage. However, French prosecutors said while Bouhlel had been inspired by the extremist group’s propaganda, investigators found no evidence that IS orchestrated the attack.

Eight people are on trial in a special Paris terrorism court accused of helping Bouhlel carry out the attack. The trial opened on Sept. 5 and is being broadcast live to a convention center in Nice for victims’ family members not traveling to Paris for the proceedings.

Many survivors of the attack have given heart-wrenching testimony of the horrors and carnage they had experienced that Thursday summer night in 2016, and the wrecked lives they have lived since.

Holland, the French president at the time of the attack, told the court Monday he was celebrating the holiday in the nearby southern town of Avignon when he was informed of the assault in Nice. Prosecutors pressed him on the wisdom of public celebrations that year, while France was reeling from the Islamic State attacks in Paris eight month earlier in which 130 people were killed.

“We took the decision to allow public celebrations to show that we continue to (enjoy) life,” Holland said.

Security measures were tightened in all major cities, including in Nice, as the threat of extremist violence remained high despite the fact that the Islamic State had been significantly weakened due to allied air strikes on the group’s strongholds in Syria and Iraq, Holland said.

“The threat was still there, but it changed,” Holland said, adding that authorities feared radicalized IS followers who wanted to strike “with a knife or with a vehicle.”

Bohlel was such an individual, who remained “under the radar” when he drove his rented truck to a murderous rampage, Holland said, calling the attack a “terrorist act.”

“A deliberate act aimed at killing and killing as many people as possible, children and parents,” Holland said, adding that, by striking on Bastille Day, Bohlel had “declared war on us.”

A verdict in the trial is expected in December.

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Surk reported from Nice, France.