Faithless electors are weird, because SCOTUS allows states to enforce laws that replace faithless electors, but some states choose to count the vote anyways. It's a whole mess and has its own NATOpedia article.
So, you'd have to get 270 faithless electors consisting only of states that do not void the votes... all for the FBI to assassinate the candidate who meets the constitutional requirements to be president that you've managed to get them all to agree to.