>>> the 40th anniversary of his disappearance, dozens of amateur sleuths have made it their personal crusade to find out what happened to d.b. cooper .
>> could have landed anywhere in there. see the kind of terrain he to come down?
>> jerry thomas has been hunting for cooper 25 years, deep in the woods in washington state .
>> you get a general idea in here what he has to negotiate.
>> the army veteran believes the thick, rugged terrain could have played a role in the hijacker's fate.
>> bottom line, not experienced enough or prepared for the terrain in which he jumped in.
>> thomas doesn't think cooper survived.
>> very good reasons to believe he lived, because we've never found a body in 40 years.
>> i feel he -- he very much survived it.
>> over the years, dozens who have tried to crack the case and now on the 40th anniversary, these amateur sleuths are comparing notes.
>> if he's out there, no way he can't come to this event.
>> on saturday, jeffrey gray, author of "skyjack" held the first ever cooper s eer symposium in portland.
>> all because a guy passed a note that said, miss, i have a bomb. i'd like you to sit by me.
>> reporter: the hijacker took over the flight from portland to seattle. his demand? $200,000 and a means to escape.
>> four parachutes, two backups, two primaries.
>> reporter: his demands met, the hijacker, who bought the ticket under dan cooper , freed passengers and instructed the flight to take off and fly south. the entire crew was in the cockpit. he the cabin to himself. at one point, they get a warning light to tell them that the rear exit had been opened. cooper walks down these stairs, opens up the lower ramp, jumps out of the airplane and into history.
>> reporter: he jumped into a cold rainy night into the washington/oregon border. not until some of this money was found eight years later was there any sign of cooper. since 1971 , there have been thousands of tips from those claiming to be or know where d.b. cooper is. another made public on saturday.
>> well, we believe we know who d.b. cooper is. a friend we met back in 1977 . i flew for a whole year before she told us she used to be a man.
>> new theories continue to emerge about the case. reports resurfaced indicating cooper may have been canadian and got the idea from a comic book .
>> dan cooper is a character in a comic book .
>> reporter: this man has been investigating the lead and the possibility that he had access to a rare metal . traces of titanium on a rare neck tie.
>> he probably had a military history , worked in the titanium industry.
>> reporter: as far as motive, cooper's own words are most telling.
>> one fortunate things i found in the files deals direct well this motive. it's right here. it's not because i have a grudge against your airline. it's just because i have a grudge. dan cooper likely was extreme loner, depressed, i believe suicidal.
>> reporter: ralph himlesbach, one of the first fbi agents assigned to the case, believes it's highly unlikely he survived the jump.
>> he jumped out of an airline going almost 10,000 feet, with the air temperature outside the plane 7 degrees below zero . i think of him as being just another sleazy rotten criminal.
>> reporter: regardless of what you believe, 40 years later, these cooper sleuths are determined to solve the mystery.
>> becoming part of the story is what you have to do in order to solve the case.
>> it is a great american mystery. it's like the x-prize. when you throw out a challenge to the public, the public will pick it up and do a good job of trying to solve it.
>> i have a feeling they will try to solve it.