As we reported here, investigators had been hopeful of laying the case to rest after tip off from a fellow law enforcement official had pointed them towards another potential candidate for the brazen hijacking.
But when they compared the DNA found on a tie with some taken from the suspect, it did not match.
However, special Agent Fred Gutt said that the test does not necessarily rule out the now deceased suspect because there are three different DNA samples on it.
He added that it's possible it had been used previously by other people and the case which has baffled law enforcement officials for almost four decades continues.
Back in 1971, a man with a ticket in the name of Dan Cooper boarded the Northwest Orient Airlines 727 flight from Portland to Mexico via Reno and sat in seat 18F.
Then, shortly after take off, the man believed to be in his mid forties ordered a bourbon and water.
But when the flight attendant returned with his drink, he handed her a note saying: "Miss, I've got a bomb, come sit next to me — you're being hijacked."
He followed us his threat by opening a briefcase which appeared to contain explosives and demanded $200,000 and parachutes.
With little choice the authorities agreed and after landing the plane at Seattle Airport, he exchanged the terrified passengers and a couple of the flight crew for the ransom.
Then he demanded that the pilots take off and head for Mexico.
About 40 minutes after takeoff, a signal light in the cockpit showed that the plane's rear stairway had been extended.
When the jet landed in Reno, the stairs were down and two parachutes, the money and the mysterious Cooper were gone.
There have been more than 1,000 suspects over the past four decades, but almost 40-years later the identity of the hijacker remains a mystery.
Some have also speculated that he failed to survive the 10,000ft leap, especially after $5,800 worth of decomposed $20 bills, identified as part of the ransom money were recovered in 1980 by a child digging on the banks of the Columbia River near the Oregon border.
But no body has ever been found and few other signs of his fate have been discovered.
However the FBI is refusing to give up and after launching a new blaze of publicity last year this latest suspect, who had not been identified before emerged.
Forensic experts are continuing to search for more fingerprints or DNA on the dead man's effects to compare with items the hijacker left behind.