A Lebanese-Canadian academic has been convicted in absentia of terrorism charges and sentenced to life in prison over a bombing outside a Paris synagogue in 1980 that killed four and wounded 46.

The court in the French capital issued an arrest warrant for Hassan Diab, who lives in Ottawa, Canada, and denies wrongdoing.

His lawyers say he was in Lebanon at the time of the attack and is a victim of mistaken identity.

The trial marked the culmination of decades of investigation into one of France’s longest unsolved crimes.

France Synagogue Attack rial
William Bourdon was the lawyer for Hassan Diab (Michel Euler/AP)

French authorities accuse Diab of planting the bomb outside the synagogue where 320 worshipers had gathered to mark the end of a Jewish holiday on the evening of October 3 1980, including children celebrating their bar mitzvahs.

French investigators attributed the synagogue attack to the Popular Front for the Liberation of Palestine-Special Operations but no one ever claimed responsibility.

The conviction was a surprise to many even in the court. Among the defence witnesses was a magistrate who investigated the case and testified that there was not enough evidence to convict Diab.

The head of France’s leading Jewish group, CRIF, welcomed the conviction, and urged Canada to arrest Diab.

The victims’ lawyers said the long-awaited trial will serve as a deterrent to other terrorist acts and antisemitic sentiments.

French authorities accused Diab of planting the bomb on a motorbike outside the synagogue on Rue Copernic.

Investigators initially suspected far-right extremists before shifting their focus to Palestinian militants.

Canada authorised Diab’s extradition to France in 2014 as part of the investigation, but after three years in pre-trial detention, anti-terrorism judges ordered him to be freed due to lack of evidence.

Then an appeals court ruled that he should stand trial on terrorism charges. Diab remained in Canada throughout the trial, which started earlier this month.

For those touched by the attack, the trial was a long-awaited opportunity to speak publicly about what happened.

Survivors described years of physical and mental trauma. Some said the sound of motorcycles haunted them after that night. Families of those killed mourned lost children or siblings.

Prosecutors argued that Diab has been lying to himself for 40 years and is caught up in his denial and escape from reality.

Diab’s lawyer William Bourdon had pleaded for an acquittal, saying that convicting someone would be “a judicial mistake”.

Amnesty International was among those which called for the court to drop what they called a flawed and baseless case, arguing that it “undermines effective justice for victims”.

Some lawyers for the 18 people and six groups that were party to the case acknowledged that it was hard to build a case so many years later, especially without the kind of DNA evidence or mobile phone data used in current investigations.