So, I finally found out what happened to my paternal grandfather.
I never knew him. My dad only remembered meeting him once. He disappeared frequently from the time he married my grandmother, and left for good before Dad was three. They met when he came back to give my grandmother a legal divorce. He was a con-man and an identity thief, we knew, but that was it beyond his actual birth and marriage/divorce records under his legal name.
Dad passed away in 2009, and at that time I was his only family that he knew of that still lived. He wanted to know not just about his father, but his own children who ended up getting adopted. He wanted his kids to know who their Dad was, even if they didn't get to know him.
I've already found my younger brother and sister -- two years after Dad died. But his own father eluded us. We knew he wasn't entirely involved in above-board activities. He hadn't been heard from since a few months after I was born. But he wasn't in any people search, and wasn't in the Social Security Death Index.
Finally, they accepted a missing persons report after interviewing his sister, who confirmed the potential that he hadn't stayed gone voluntarily if he left -- people came looking for him, claiming to be from the FBI, saying they had a material witness warrant for him. But they had no records of him in prison.
The US Marshals compared our family's DNA to several bodies where they knew the subject had engaged in identity theft, including the strange case of "Joseph Newton Chandler".
Finally, yesterday, the Marshal in the Chandler case confirmed my grandfather's final identity and resting place. He died as Robert Stuart, in 1998. By then he was forced to use his real Social Security number to claim SSI, as he'd suffered some kind of amputation and was in a nursing home. They confirmed most of of the information we thought we knew about him was correct.
And now I can go visit his grave.
https://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=34246143
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... find the identity of "Mr. Chandler".
Because I had been on the Doe Network doing searches for him for years, I knew about the case. We knew he had ties to California, but the closest we knew to my grandfather having any experience in the Navy was he'd said he'd worked on oil rigs. Still, there was far more we *didn't* know than we did.
It was sorta surreal when the first call came where they saw my grandfather as a possibility for "Chandler" -- the case us so unusual it's led to speculation he might have been the Zodiac Killer. 
Yesterday's call... I was crying. I knew they had other places that those resources needed to go. But then again it might not have been that hard for the Marshals, considering the higher level of access to federal databases they have.
Thanks for posting about your family's history and your quest. 
Found one side of my family's trip over from what was then Prussia. 
Though, remember it is the LDS database and connects with other people's trees. If you get into a particularly traced tree, you might be able to see claims where you can trace yourself to Adam and Eve. Seriously. I did. Heh.
