IF LBJ KILLED JFK THEN WHY DID HE NOT RUN FOR POTUS IN 1968?

If, as Dodgy Roger Stone proposes, it was LBJ who killed JFK, then as long as he was POTUS he could continue to cover up his crime.

So why did he not run for a second term as POTUS in 1968?

By not running he relinquished power over the cover up (assuming that it was him) and thus risked being exposed.