Yup, with the right warrants they could try to trace the IP address from which the e-mail was sent. And find most likely a public wi-fi server, an unsecured private wi-fi network belonging to an innocent third party, or a computer at a public library, or possibly that the e-mail was sent from a big online e-mail service that was logged into via onion routing if the sender was really tech savvy.
Of course if the perp is an idiot and sent it from his home or work computer. . .
liberal...idiot.....aren't those two words synonyms?