Police hunting a serial rapist in the French city of Marseille have used DNA evidence to arrest two men, but are unable to say which is the culprit because the pair are identical twins.
Investigators face having to run extensive tests costing up to a million euros to distinguish between the 24-year-old brothers' genetic codes, which are so similar that normal DNA tests cannot tell them apart.
"It's a rather rare case for the alleged perpetrators to be identical twins," said Emmanuel Kiehl, the chief investigator in the case. "We must determine the exact role of each one." He added that current techniques for identifying the differences between DNA of identical twins were onerous, costly and rarely conducted in French laboratories.
Kiehl said the victims, six women between the ages of 22 and 76, had formally identified their assailants from photographs, but they 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 six women between September and January. The frequency of the attacks increased rapidly at the beginning of the year, with three committed in the space of three weeks.
The 76-year-old woman was the first victim. After being injured by her attacker, she was forced to perform a sex act.
Each rape took place at night, with the attacker striking in the entrance hall or stairwell of a building. The assailant also took the victims' mobile phones.
With the help of video footage, a traced telephone belonging to a victim, and positive identification from the victims, local police were led to one twin. They then discovered that he lived with his identical brother.
"The seriousness of the crimes necessitates that an expert genetic examination is now launched and financed," a source working on the case told the French newspaper Le Parisien.
Investigators are going through with plans to complete the "enormous" job of decoding the DNA of the suspects, then comparing it to DNA found at some of the crime scenes, which reportedly matches the twins' "common DNA".
La Provence, a local newspaper, reported that police were told it could cost up to euros 1?million (pounds 846,000) for the necessary tests. It quoted a DNA expert saying that only the smallest of differences existed in the DNAs of identical twins. "For a normal analysis we compare 400 base pairs," the expert said, adding that with twins: "We would be looking at billions."
Scientists have demonstrated that differences in the DNA of identical twins exist. However, the process of decoding those differences is "expensive and not fully developed and remains confined to research laboratories," said Catherine Bourgain, a specialist on the issue at the French National Institute of Health and Medical Research (Inserm).
The twins were described as being of mixed minority and Caucasian origin. "They are real identical twins, nothing really distinguishes them, and they repeatedly use and lean on the fact that they are twins," said another source on the case.
The twins, who are being held in custody, are unemployed and are said to share mobile phones often.
