French police are having trouble telling which identical twin is wanted for a series of sex attacks on young women in Marseille.
Both twins have been arrested but police say they can't determine the culprit since the twin's DNA is identical and the victims can't tell the two apart, reports the Independent.
Police said DNA found on the victims matches that of the 24-year-old twins, named as Elwin and Yohan, but that they can't prove which twin -- or possibly both of them -- committed the crime.
Standard DNA tests are unable to tell the difference between the strands of identical twins.
According to the BBC, police in Marseille were told it would cost upwards of $1.3 million for a genetic test sophisticated enough to tell one set of the twins' DNA from the other.
"For a normal analysis, we would compare 400 base pairs (of nucleotides), which make up DNA," an expert told French newspaper La Provence, reports UPI.
For identical twins, "we would be looking at billions."
It's not the first time police have been stumped about which twin committed a crime.
Orlando Nembhard, 19, was thought to have killed a man outside of an Arizona nightclub in 2011.
He was freed after his attorney claimed the shooter could have been Nembhard's twin brother Brandon, who was also present.
Witnesses were unable to tell the two apart and police dropped the case, reports the Huffington Post.