LUCASVILLE, Ohio -- Ohio on Tuesday executed a condemned killer who claimed he was innocent of stabbing a woman 138 times, slitting her throat and cutting off her hands.

"I'm good, let's roll," Brett Hartman said.

The effect of the single dose of pentobarbital did not seem as immediate as in other executions at the state prison in Lucasville. Four minutes after Hartman first appeared to be reacting to it as his abdomen began to rise and fall, his abdomen rose and fell again, he coughed and his head shifted rhythmically for a few moments.

Hartman was the 49th inmate put to death since Ohio resumed executions in 1999. The U.S. Supreme Court denied a last-minute appeal Hartman on Monday.

Amnesty International says only China, Iran, North Korea and Yemen executed more people than the U.S. last year.

Hartman, 38, acknowledged that he had sex with Winda Snipes early on the morning of Sept. 9, 1997 at her apartment. He also says he went back to Snipes' apartment later that day, found her mutilated body and panicked, trying to clean up the mess before calling police.

But Hartman said he didn't kill her, a claim rejected by numerous courts over the years.

The Ohio Parole Board had unanimously denied Hartman's requests for clemency three times, citing the brutality of the Snipes' slaying and the "overwhelming evidence" of Hartman's guilt.

Hartman's attorneys have long said that crucial evidence from the crime scene and Snipes' body had never been tested, raising questions about Hartman's innocence. The evidence included fingerprints allegedly found on a clock and a mop handle. Hartman also argued the evidence could implicate an alternate suspect.

The attorneys had argued that if Hartman's innocence claim wasn't accepted, he should still be spared because of the effects of a "remarkably chaotic and nomadic early childhood," including being abandoned by his mother and left with an aunt on an isolated Indian reservation.

The state opposed those arguments, citing the strength of the evidence and the fact that courts have repeatedly upheld Hartman's conviction and death sentence. The state also said Hartman refused to take responsibility and show remorse.