The mass screening, believed to be the first time police have used DNA in a suspected infanticide case, was criticised yesterday by a civil liberty group as "so coercive it might as well be compulsory".
Detectives are writing to the parents of girls in Warrington, Cheshire, asking for permission to carry out the tests. The baby boy's body was found dumped in a bin bag three weeks ago in a wood close to a theme park on the outskirts of the town. The infant had been strangled within two hours of birth.
A police spokesman said the testing would involve mouth swabs. Girls as young as 12 will be included in the testing. "It is a process of elimination that is vital to any inquiry. We want to eliminate everything on the periphery so we can focus on the nub of the inquiry."
Police are still hunting two men aged around 18, one of them carrying a bin liner, seen near the spot where the body was discovered.
John Wadham, director of Liberty, said: "This approach must seem even more coercive to teenage girls that it would to adults; they will be under pressure not only from the police, but also from their school and their parents - it must be almost impossible for any of them to refuse."Reuse content