Looking for input from someone with LE background.
Assuming this case is solved, and those responsible are convicted, what happens to those who knew something but did not come forward? Would they be charged as accessories to murder, even though they may not have participated in the planning or execution of the crime? Or would it be considered obstruction of justice?
This assumes after all the available evidence is presented, including autopsy results, forensics, phone records, etc. that it becomes obvious what the friends or relatives of those accused knew, or should have known, more than they were willing to share with LE.
These are all good questions. In regards to what happens to those who knew something but did not come forward, it depends. They could be charged with interfering with the investigation, especially if they were previously interviewed, and did not come forward with useful information. If they were asked specifically about something and denied knowledge, and it is later proved that they were not truthful or forthcoming, they will most likely be, at a minimum, charged with interfering with an investigation. If they were a witness, they can be charged with capital murder as well, depending on the state, as they did nothing to prevent the crime, and did not report it soon thereafter. This could possibly dissolve into a second degree murder charge. If they had any part in concealing evidence, there is another charge. Obstruction of justice is always a possibility as well, but if the prosecution is serious about justice, they will go for the more serious charges. Also, in cases where murders are premeditated, if someone was aware of the plan, and did nothing to prevent it, they are just as guilty as the offending party, if this can be proved. It is also to be considered that other crimes may have taken place as well, such as kidnapping, robbery, rape, not to mention the obvious arson. Any person privy to any of these crimes faces myriad charges, which is one reason why our justice system allows for plea agreements, to allow for persons who may not have had intent to commit a crime, but to have became involved by situation or circumstances, to assist law enforcement by providing unknown information or evidence that they need to secure a conviction of the primary perpetrator.
By coming forward, a person has the opportunity to possibly avoid serious charges, if they are willing to cooperate. It may be a matter of avoiding prosecution completely, or possibly to face lesser charges. It all depends. There is no black/white in the justice system. It's all one big grey area, and it is chess, not checkers, so everyone has to play the right piece, at the right time. This goes for the criminals, witnesses, victims, LE, prosecution, defense attorneys, feds, judges, and so on.