Knowledge, alibi, DNA, experience, physical characteristics...a lot of stuff points to Sheridan.
Okay, if you don't mind expanding just a bit:
Knowledge - What knowledge? How to jump out of a plane into forest? Got it. How to jump out of a 727? Speculative, no?
Alibi - have you punched holes in one? Is there a lie you are able to prove pertaining to one? So far I have only heard that he was abroad for a few years.
DNA - that the FBI didn't clear him based on it? A DNA match would have led to an arrest. The DNA they have (epithelial, from the tie clasp) is dubious at best. But they also have hair. Take a look at this article from just a few months after Case Closed:
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They can now isolate and identify the proteins in an individual's hair, and match them against the genes that would code for those proteins. They already have the means and the knowledge to close the case if it's Peterson. And to stop inquiries from nuts like us.
Experience - not experience committing crimes. See "Knowledge" above.
Physical characteristics - bald with blue eyes. You need to place colored contact lenses on him in 1971 or get Schaffner to retract a 50 year old statement about piercing brown eyes. Then you need to get all of the witnesses to give opinions about hairpieces and whether or not Cooper could have been wearing one. Height and age seem to be all you've got.
I personally would like to eliminate as many potential suspects as possible. I would start with Rackstraw and Dayton, who would probably be the easiest to eliminate. Does that mean, since I am investigating them, that I consider them strong suspects? No. It means I am using a process of elimination. The FBI asking for Peterson's DNA is only significant in that they had such little evidence on the guy that they needed his DNA in order to do so. You want them to clear him, your best shot is this book of yours. Because the only thing that got them to clear the other two was public pressure, which translates to "Jesus, I can't get any real work done with all of these phone calls and letters coming in about LD Cooper. Can we just get these assholes off my back already?"
These are great probing questions, all of which I can answer.
1) KNOWLEDGE: This is no small matter. Cooper demonstrated he knew a lot about the 727 including the following: it had a unique 15 degree flap setting, where the oxygen bottles were located, that it takes about 20 minutes to refuel, and very importantly, the the aftstairs could be deployed in flight (no squat switch) or take-off with them down and that the jet could actually fly with them deployed (no flight control problems). I have unaware of a single pilot from that time frame who knew that the airstairs could be deployed during flight. In fact, the pilots of 305 and Northwest Flight Ops in Minneapolis weren't aware that the jet could fly as Cooper demanded, yet DB Cooper did. Unless, of course, he just guessed and happened to guess correctly.
The above, plus the tie particle evidence discovered by the Cooper Research Team in 2008 and 2017 strongly suggests DBC was either a Boeing employee or someone very close to Boeing with access to certain data about the 727 that was not easy to come by and in some cases restricted.
Skydiving is also a critical component. Just leaping out of the jet at night, 10,000 feet up take some stones. Not getting killed takes skill. Also, he knew how to don and use the parachute. In fact, when offered an instruction card he turned it down. This strongly suggests that DB Cooper knew what he was doing. Unless, of course, he just guessed and happened to guess correctly.
Sheridan Peterson meets the criteria established above. The universe of people who meet this criteria is going to be limited.
2) ALIBI: The fact the the event took place the day before Thanksgiving is a blessing. Most people celebrate Thanksgiving with other people which went along way toward helping the FBI establish alibis for suspects.
Sheridan Peterson was not just overseas...for example in London where establishing his whereabouts would be relatively easy...he was in Nepal. According to him, living in a mud hut (which is an overstatement). The problem is that the FBI has not been able to verify where he was, not even what part of the world he was in, during the hijacking. Sheridan says he was in Nepal but can't prove it, in part because he wasn't employed for the 2 1/2 years he lived there.
The problem for Sheridan is that he says he was in Nepal for the entire 2 1/2 years...didn't leave the country. Well, he did not show his passport to the FBI for one. Also, the fact that he claims to have lived off the proceeds of a numbered bank account based in Singapore that he established in 1971 is very problematic. If this is true (and there is no reason to think that the essence of the story isn't true) it blows his alibi because he would have had to travel out of Nepal to open the account in 1971. Plus, given the requirements associated with numbered accounts one must ask where he came up with the money to open the account in the first place. Of course, were not even addressing the other obvious question: Why would you need to open an account that is numbered, secret, confidential and hidden from the authorities to begin with?
3) DNA: The Cooper DNA is partial and was not derived from epithelial skin cells. Rather, it was derived from a saliva sample on the tie. To be sure, the FBI lost the eight cigarette butts and I have no idea what happened to the two hair samples they collected. Nonetheless, they have established a partial DNA (I'm not certain how strong...I've asked to no avail) and have felt it important enough to compare three suspects. Two of those suspects, Weber and LD, arguably were tested, in part, because of intense pressure. Notably, these two suspects have been publicly cleared by the FBI by virtue of their DNA.
The third suspect to have a DNA comparison, and the only one that the FBI actually sought was Sheridan Peterson. Additionally, he has not been publicly cleared by the FBI by virtue of his DNA or for any other reason. I have tried multiple times to get some straight answers regarding this but have been rebuffed each time.
4) EXPERIENCED CRIMINAL: When I established my profile for DB Cooper it involved someone who was not a criminal with a record. Rather, DBC struck me as someone pushed to the limit personally who was looking for a creative way to get out of a bind. Also, the fact that DBC has never been caught tells me two things: First, he didn't try it again. Two, he didn't talk about it. Frankly, career criminals aren't that smart.
5) PHYSICAL CHARACTERISTICS: Arguably the first FBI sketch is remarkably close in appearance to Sheridan Peterson. Moreover, he fits the basic metrics; 6'1", black hair, high forehead, mid-40s, fit, no discernible accent. The FBI is not certain whether DBC had blue eyes. After all, their description says "possibly brown" for an eye color. Also, this is based off of a very brief encounter at the beginning of the flight when there was nothing unusual going on. Florence also told the sketch artist that she could not be certain about certain aspects of his eyes. Considering this encounter took place in a jet cabin with limited lighting any ascribed eye color is dubious.
The thin hair is not a terribly big issue. Sheridan Peterson was not bald. We have plenty of picture showing he has hair on his head, albeit thin. But considering he may not have had a close hair cut recently, his hair would be consistent with some of the descriptions given by witnesses, which, frankly have been quite diverse.
Of course, there are many other things that point to Sheridan, including the words of his ex-wife if they can be verified. To reiterate, the FBI itself has been very intrigued with the man for decades and is still unwilling to discuss anything related to Sheridan.
