Real Life Identical Twin Criminal Law Conundrum

French police know that one of two identical twins committed a series of sexual assaults but cannot tell which.

Conventional DNA testing cannot tell the two apart.  (There is a very expensive test that might distinguish between them, but it costs 1 million Euros.)

Bruce Schneier notes, "both have been arrested in the hope that one may confess or implicate the other" (i.e., a real world Prisoner's Dilemma).