About 100 officers and staff at Paris’s police headquarters on the Seine are to be DNA tested this week in an unprecedented move by judges investigating the alleged rape of a Canadian tourist in the building last year.

Two police officers from Paris’s elite anti-gang-crime squad were charged last year after a 34-year-old Canadian woman filed a complaint that she had been raped by a group of officers. Both deny rape. One admitted to having had sex, but said it was consensual.

The accused are also facing an investigation into tampering with the scene of a crime. Another police officer was made an “assisted witness”, meaning he will be called to testify but is not under suspicion.

Judges are looking to match the DNA of a third man that was found on the woman’s clothes.

The woman says she met the off-duty police officers at an Irish pub where they had been out drinking one evening in April 2014. She made a complaint later the same night that they had raped her at their headquarters across the river from the pub.

A spokesman for the police union Synergie said the DNA testing and the dramatic staging of it was “stigmatising” to all officers at the headquarters.

The case, in which French police were accused of a gang-rape inside their own building, shocked France. The interior minister, Bernard Cazeneuve, said the two officers would “face the full consequences” if they were found guilty.

The police headquarters, known for its address, 36 Quai des Orfèvres, close to Notre Dame cathedral, was for years the base of Paris’s detective branch, the equivalent of London’s Scotland Yard, and inspired numerous crime novels and films. It was made famous by the Maigret novels written by Georges Simenon between 1930 and 1972.

The headquarters has been at the centre of several scandals in recent years. Last year a police sergeant from the anti-drugs unit was placed under investigation on suspicion of stealing 52kg of cocaine worth €2m from a secure room where the drugs had been placed after they were seized in a raid.