STOCKHOLM (AP) — Swedish artist Lars Vilks, who had lived under police protection since his 2007 sketch of the Prophet Muhammad with a dog’s body brought death threats, has died in a traffic accident, police said Monday. He was 75.

Vilks and two plainclothes police bodyguards were killed in a head-on crash with a truck on Sunday afternoon, said Carina Persson, police chief for southern Sweden. All three died on the spot. The truck driver was flown to a hospital with serious injuries.

She said the police car, which had left Stockholm and was heading south, veered into the path of the truck and both vehicles burst into flames. The accident occurred near Markaryd, some 108 kilometers (67 miles) northeast of Malmo, Sweden’s third largest city.

“There is nothing else for now that indicates that it was something else but a traffic accident,” Persson told a press conference.

“The work with the investigation is believed to take a relatively long time,” said Sweden’s top police chief Anders Thornberg.

Since 2010, Vilks had been forced to live under police protection “due to the fact that he made use of his freedom of expression and his artistic freedom,” said Sweden’s Culture Minister Amanda Lind, calling his death “an extremely tragic traffic accident”

Vilks was largely unknown outside Sweden before 2007, when he drew a sketch of Muhammad with a dog’s body. Dogs are considered unclean by conservative Muslims, and Islamic law generally opposes any depiction of the prophet, even favorable, for fear it could lead to idolatry.

Al-Qaida put a bounty on Vilks’ head. In 2010, two men tried to burn down his house in southern Sweden. In 2014, a woman from Pennsylvania pleaded guilty in a plot to kill him.

In 2015, Vilks attended a free-speech seminar in Copenhagen, Denmark, that was attacked by a lone gunman who killed a Danish film director and wounding three police officers. Vilks, widely believed to have been the intended target, was whisked away unharmed by bodyguards. The gunman later killed a Jewish security guard outside a synagogue and wounded two more officers before he was killed in a firefight with police.

Police said at this time they did not know why the car drove into the wrong lane but they were investigating whether a tire might have exploded. The car transporting Vilks had puncture-proof tires, police said. However, exploded tire remains were reportedly found on the road.

Born in 1946 in Helsingborg in southern Sweden, Vilks worked as an artist for almost four decades, and rose to fame for challenging the boundaries of art through several controversial works.

His most famous pieces included “Nimis” — a sculpture of driftwood built without permission in Sweden’s Kullaberg nature reserve — as well as three Prophet Muhammad drawings, including the one that showed the prophet as a dog.

Vilks initially planned to display the drawing at an exhibit at a Swedish cultural heritage center, but the drawing was removed after the center cited security concerns.

It went largely unnoticed until a Swedish newspaper printed the drawing with an editorial defending the freedom of expression.

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Jan M. Olsen in Copenhagen, Denmark, contributed to this report.