Updated

DNA evidence has helped French police chasing a serial rapist arrest two suspects, but they’re finding it difficult to determine which man is to blame as the two are identical twins.

Police in the city of Marseille are holding both brothers without bail while they run extensive genetic tests to try to distinguish between the two 24-year-olds, according to the British newspaper, the Telegraph. The complicated tests — which could cost more than $1 million — are a financial drain and highly unusual.

"It's a rather rare case for the alleged perpetrators to be identical twins," said Emmanuel Kiehl, the chief investigator in the case, speaking to French media.

Police say the six female victims -- ages 22 through 76 -- formally identified their attackers from police photos, but the women also could not tell the difference between the twins.

The suspects, identified only as Yohan and Elwin, denied accusations they raped and sexually assaulted the women between September and January.

The first victim was a 76-year-old woman, who was injured by her assailant and then forced to perform oral sex.

Police were able to trace one victim’s stolen cellphone, and through video and positive identification from the victims, they found one twin. Then they discovered he lived with his identical brother.

Investigators now need to decode the suspects’ DNA and compare it to that found at some of the crime scenes.

The brothers — both unemployed deliverymen — have stuck to the same defense. One of the women identified her attacker in a video taken on a bus. Only one twin positively identified himself in that video.

Click for more from The Telegraph.