The resistance to relying on DNA evidence is being replicated in other states where prosecutors believe scientific data is being relied upon to the exclusion of other evidence and letting the guilty walk free.

State prosecutors in Alabama, Arkansas, Colorado, Louisiana, Michigan, Mississippi and New Mexico have opposed requests for testing, arguing that the results would not establish innocence even if they were positive, Barry Scheck, the co-founder of the Innocence Project at the Cardozo law school in New York, told the New York Times.

More than 130 Florida inmates have been freed by DNA testing in the past 15 years. But in 2001 the state legislature set a two-year deadline for DNA retesting in older cases, sending lawyers on a race to make representations on behalf of clients who insist scientific evidence could prove their innocence.

Prosecutors concede that DNA testing is increasingly reliable, but say its relevance to some cases can be exaggerated. They make the distinction between proof that the accused may or may not be linked to a piece of biological evidence and proof that they are innocent of the crime.

Defenders say the prosecutors are trying to short-circuit an important method of establishing innocence when the results do not fit their case.