(TELEGRAPH) — Police have started conducting mass DNA tests of 527 male pupils, teachers and staff at a French high school following the “rape in the dark” of a teenager in the school toilets.

Detectives have asked 475 pupils, 31 teachers and 21 other staff present at a private lycée in La Rochelle, western France, on the day of the sex attack permission to take DNA samples from mouth swabs in an attempt to find the mystery rapist after months of fruitless searches.

The tests began this morning on adults and pupils aged 15 to 18. They were expected to last another two days at Fenelon-Notre Dame lycée, where a 16-year-old was sexually assaulted last September in a rest room.

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