If the email was sent from a Yahoo/Google/Microsoft email account, it's IP was logged, meaning if the person was using their home internet, you can get a trace

If the email was sent from a Yahoo/Google/Microsoft email account, it's IP was logged, meaning if the person was using their home internet, you can get a trace to their house with a warrant. If the email was sent from a private domain, they're traceable in many more ways. It might be a wasted effort, but you should still try. If the police don't want to give you the time, bring your lawyer in with you... they'll have the time then.