Try using Gale's "Topic Finder" to come up with keywords and subtopics.
You should also try asking ChatGPT for keywords about your topic. [sample]
What are some of the key terms related to X?
What subtopics should I know if I’m researching X?
What are some of the subtopics I should consider if I'm researching X?
YouTube is another great resource to search for recorded footage of the investigation, interrogation(s), and/or trial, or interviews of surviving victims, suspects, witnesses, law enforcement officials, and/or lawyers.