Man dies while in police custody, DA won't prosecute, what options does the family have?
Hire an attorney for civil rights violation. You will need to prove the cause of death via an autopsy, and hire a police practices expert to prove a violation of police guidelines. Probably have expenses of $10,000 to 20,000. Good luck.
You can sue, but there will have to be facts and evidence somehow showing the 'fault' of police. That will require medical experts, etc. If serious about pursuing this, feel free to contact me. You immediately need to initiate discovery to avoid evidence melting away into history.