The FBI feared that this martial-arts buddy might have known OlderBro Todashev was a US asset at one time, which would have made it seem like the FBI shared at least some culpability for the Boston Bombing.
When instead, like Icarus flying too closely to the Sun, he had been flipped by those he had started out seeking to infiltrate and had gone rogue.
So with this guy there was only one way for the ChurchBurners to be sure he stayed quiet.
Just noticed your posts here stopped in Jan 2020 when Covid was in full rampage and Wuhan was locked down.
Why would a “US asset” as you claim, buy a one way ticket to Russia?