I would look into John Podesta and those who handled his dirty work.
Podesta might have ‘ordered it’, and the actual deed may have been done by disposable people (yes, murdered to cover up the murderer), but that isn’t the story.
The real story is the Motive and the Cover-up. The FBI has all of the answers to those questions, including the cover-up. The laptops (which they denied having for 4 years) have the ‘Why’ and the people connected with denying FOI are the coverup. I suspect it goes all the way to the same guy who ordered the Russian collusion conspiracy.
What I read is that they hired it out to the local MS-13 gang. They might have even brought in a couple shooters from LA or somewhere else.