Sounds like an 18USC242 action to me. If convicted I hope these cops do get the needle.
I detest most cops and believe that a substantial number are enamored with the power and authority that their badge grants them.
Nevertheless, these crimes occurred during an incredibly stressful event where the cops panicked and made poor decisions. 1st degree murder requires premeditation, and there is no evidence of that. These cops should be tried and convicted for manslaughter or negligent homicide, as well as for the cover up. Executing these cops would be an even greater abuse of justice than that which they committed.