DNA testing from a new suspect believed to be D.B. Cooper doesn't provide a match to the necktie the hijacker left behind on the jetliner in 1971, according to the FBI.
Special Agent Fred Gutt has warned that the test doesn't necessarily rule out the dead suspect
Gutt told the Seattle Times that there are three different DNA samples on the tie and that it's unclear where the hijacker got it.
"There are some questions about the tie itself: Was it a used tie, a borrowed tie?" Gutt said.
Marla Cooper, an alleged niece of the hijacker, recently came forward and said she had a role in renewing the FBI's probe into the 40-year-old case.
Marla Cooper told ABC News she is sure that her uncle Lynn Doyle Cooper is the one who pulled off the notorious 1971 hijacking by threatening to blow up a commercial jetliner before leaping from the airplane with a parachute and $200,000 in ransom.
Marla Cooper said she is certain after clarifying childhood memories about the incident and through recent conversations with her parents.
She recalled being 8 years old and hearing her two uncles making suspicious plans at her grandmother's Oregon home near where D.B. Cooper jumped.
"My two uncles, who I only saw at holiday time, were planning something very mischievous," she told ABC News. "I was watching them using some very expensive walkie-talkies that they had purchased. They left to supposedly go turkey hunting, and Thanksgiving morning I was waiting for them to return."
One day later, Northwest Orient flight 305 was hijacked, and her uncle L.D. Cooper came home and said he was in a car accident.
"My uncle L.D. was wearing a white t-shirt and he was bloody and bruised and a mess, and I was horrified. I began to cry. My other uncle, who was with L.D., said Marla just shut up and go get your dad," Marla said, doubting there was ever a car accident, but that her uncle was the parachuting criminal.
"I heard my uncle say we did it, our money problems are over, we hijacked an airplane," she added.
Marla has provided FBI agents with a guitar strap and a Christmas photograph of her uncle picture with the same strap.
Federal investigators have checked hundreds of leads since D.B. Cooper parachuted from the flight with the ransom money.
The FBI recently said it was looking into a promising new lead from a retired law enforcement official that a man who died 10 years ago in the Pacific Northwest is Cooper.