Final answer:
The case that the police opened to keep Watts in prison is not specified in the given information. More context or specific details are needed.
Step-by-step explanation:
The case that the police opened to try to keep Watts in prison is not specified in the given information. It seems that Watts and Darren are waiting in prison for a trial, but the reason for their imprisonment is unknown. More context or specific details are needed to determine which case the police opened to keep Watts in prison.