The Albuquerque office of the medical examiner said this week it couldn't determine the identity of the human femur found in 2011.
However, the Federal Bureau of Investigation says the "weathered" bone has been sent to an FBI lab for more tests and investigators aren't given up on possible connections.
The FBI and Albuquerque police are looking for any remains of missing victims of David Parker Ray.
Authorities have long believed Ray, who died in 2002 while serving life in prison for sexual torture, buried some of the 40 victims he claimed to have had.
No bodies have ever been found.