CLEVELAND – A man who wrote hundreds of hateful letters to black and mixed race men seen with white women apparently was motivated by a girlfriend who left him for a black man, the FBI said Friday.

David Tuason, who is of Filipino descent, admitted his motive when he was captured two months ago, said Frank Figliuzzi, the head of the FBI in Cleveland.

“One of the first phrases out of his mouth was, 'You wouldn't understand 'til it happened to you,' and when they inquired what that meant, he said, 'My girlfriend left me for a black man,'” Figliuzzi said.

The FBI was surprised that a jilted man was behind the hundreds of letters that went to, among others, Supreme Court Justice Clarence Thomas and New York Yankees shortstop Derek Jeter.

In many of the letters sent over 20 years, he posed as an angry white woman threatening violent acts such as castration or explosions at buildings.

FBI agents arrested Tuason on March 14 after tracking e-mails sent from a public library. The agency's behavioral experts had developed several theories about the letter writer, but a jilted lover wasn't in the mix, Figliuzzi said.

“It's a lesson in considering the obvious,” he said. “You can overcomplicate profiles and assessments and when you arrest the guy, he says, 'My girlfriend left me for a black man.'”

Tuason, 46, plead guilty Thursday to six counts of mailing threatening communications and two counts of threatening interstate communications. He could receive up to 10 years in prison for writing a threatening letter to a Supreme Court justice and five years on each of the other charges.

Tuason will be sentenced July 24. His defense attorney, Donna Grill, declined to comment. The Tuason family attorney didn't immediately return a call Friday seeking comment.