The family of these deceased are not to smart or not heart broken enough or mad af for revenge, etc. To catch a killer you must........
UP THE REWARD MONEY.
They must come together and to an agreement and come up with AT LEAST 100K or more to catch these killers. When the pool of money is big enough people will snitch, talk, rat, tell, etc. Somebody knows something but the reward is not big enough to take the risk and tell, so hush hush for now. Someone out there knows something and they need the money also.