Steven Frederick Spears died after an injection of the barbiturate pentobarbital at the state prison in Jackson, warden Eric Sellers told witnesses.

Spears, 54, was convicted of the August 2001 murder of his ex-girlfriend, Sherri Holland, at her home in Dahlonega, about 65 miles north east of Atlanta.

Spears did not make a final statement and declined to have a prayer read. Within minutes of the drug beginning to flow, he took several deep breaths and swallowed a few times before becoming still.

Georgia has executed more people this year than any other state, including Texas which has executed seven. Three other states - Alabama, Florida and Missouri - have had one execution apiece, for a nationwide total of 18 this year.

Eight is the most executions Georgia has carried out in a calendar year since the death penalty was reinstated in 1976. The state executed five inmates last year and five in 1987.

A Georgia Supreme Court summary of the case said Spears killed Ms Holland because he suspected she had become romantically involved with someone else. He came up with four separate plans for her death and ultimately killed her by choking her, wrapping tape around her mouth and face and putting a plastic bag over her head, the summary said.

Spears told investigators he told Ms Holland when they began dating that if he caught her or heard that she was sleeping with someone else he would choke her to death. Towards the end of his confession, he said: "I loved her that much. I told her I wasn't letting her go, and I didn't."

He added that he would do it again if he had to.

Spears did not help his lawyers during his trial and automatic direct appeal and refused to initiate any post-conviction appeals.

About 10% of inmates executed in the US have voluntarily waived their appellate rights, although Spears was the first case in Georgia, said Robert Dunham, executive director of the Death Penalty Information Centre, a non-profit group.

"These executions are always problematic because they are cases in which there has not been complete judicial review," Mr Dunham said, adding that the types of errors that typically result in a death sentence being overturned are frequently unearthed in post-conviction proceedings when a new team of lawyers digs into the case.

There have even been cases in which inmates who waived their appeals changed their minds at the last minute, halting their executions, and subsequently had their death sentences overturned, he said.

Lawyer Brian Kammer, executive director of the Georgia Resource Centre, which defends death row inmates, filed a petition on Monday saying there were constitutional violations during Spears's trial and arguing that he was not mentally competent to make the decision not to pursue appeals.

Spears told Butts County Superior Court Judge Thomas Wilson during a hearing on Tuesday that he had been tested and judged competent and argued he had the right not to pursue appeals, according to a transcript. Lawyers trying to fight his execution were "trying to force their beliefs on me", he said.

Mr Kammer asked the judge at a hearing on Wednesday to dismiss the petition after two experts found Spears had the capacity to make a rational choice regarding legal challenges.

He said prosecutors had assured him that if Spears changed his mind, the execution would be halted and Spears would be allowed to contact lawyers who would be waiting with appeal paperwork for him to sign, according to a transcript.

When the state's expert, Dr Matthew Norman, asked during an evaluation on Tuesday if he wanted to die, Spears said: "Not really, but would you want to live in a six by nine cell? That's not living," according to the psychiatric evaluation report.

He added: "I want to because I don't want to live like I'm living. It's like a cancer eating me up every day."

When Dr Norman asked about his refusal to pursue appeals, he said: "We're talking about another 10 to 15 years. I'm not doing that. The process takes so long. It's what's wrong with the death penalty. I have another 20 years of appeals."