According to the complaint, Gimbel admitted to sending the first message when officers interviewed him at his home. He said his intention wasn't to hurt Obama, but rather to get attention.
Gimbel was warned that he'd be prosecuted if he sent more messages. But apparently he couldn't help himself.
And it sounds like the email messages aren't the only evidence of Gimbel's volatility. When authorities were seeking an arrest warrant, they asked to be allowed to enter Gimbel's house without knocking, citing the facts that during an earlier arrest, he had been found by sheriff's deputies with a loaded handgun, and that some of his earlier emails included threats against law enforcement.