WASHINGTON, Sept. 5 ? In his final years in prison, Kirk Bloodsworth had a passing acquaintance with a fellow inmate, Kimberly Shay Ruffner. Mr. Bloodsworth, a prison librarian, delivered books to Mr. Ruffner. Sometimes they lifted weights together. But Mr. Bloodsworth said Mr. Ruffner seemed to behave "kind of peculiar" when they were together.

Mr. Bloodsworth may now know the reason why. This morning, the police in Baltimore County charged Mr. Ruffner in the murder and rape of a 9-year-old in 1984, Dawn Hamilton, the very crime that Mr. Bloodsworth was serving time for when he met Mr. Ruffner.

"I'm so happy," said Mr. Bloodsworth, 43, a fisherman from Cambridge, Md. "This tells the world that I'm innocent."

The charges against Mr. Ruffner open a new chapter in a case that has become a prime example of the two-edged nature of DNA testing: not only as a means of clearing the wrongly accused, but also of identifying new suspects in cold cases.

In 1993, Mr. Bloodsworth became the first person in the nation convicted in a death penalty case to be exonerated through DNA testing, which eliminated him as a source of semen stains on the girl's underpants. He had served nine years in prison, including two on death row, when he was released by a judge and pardoned by the governor.

…Defense lawyers say they hope the dual use of DNA evidence in the case will reduce resistance among prosecutors to allow prisoners to challenge convictions with DNA tests. They say the case demonstrates that DNA can not only prove innocence, but also pinpoint culprits.

…The new charges were filed at a crucial time in a debate in Florida over a law from 2001 that will soon bar prisoners from seeking DNA testing for old cases. The law set Oct. 1 as the deadline for such requests. It also allows the destruction of DNA evidence, except in death penalty cases.