LUCASVILLE, Ohio (AP) – Ohio executed a killer yesterday by performing the nation's first lethal injection using a single drug, a supposedly less painful method than previous executions that required three drugs.

Kenneth Biros was pronounced dead at 11.47 a.m. yesterday, about ten minutes after one dose of thiopental sodium began flowing into his veins at the Southern Ohio Correctional Facility in Lucasville. The US Supreme Court had rejected his final appeal about two hours before.

Experts predicted the thiopental sodium would take longer to kill the 51-year-old Biros than the convention three-drug cocktail, but the ten minutes it apparently took him to die was about the usual length of time even under the method previously used by Ohio and still used by most other death penalty states.

The mother, sister and brother of Biros' victim, Tami Engstrom, applauded as the warden announced the time of death.

"Rock on", Debi Heiss, Tami's sister, said a moment earlier as the curtains were drawn for the coroner to check on Biros. "That was too easy".

The execution team tried for several minutes to find usable veins, including inserting needles several times in both arms, before eventually completing the process on just his left arm after about 30 minutes.

After the chemical started flowing at 11.37 a.m., Biros' chest heaved up and down several times, and he moved his head a couple of times over about two minutes before his body stopped moving.

Prisons director Terry Collins said the team took as much time as needed and he considered the process problem-free.

Ohio overhauled its procedure after a failed attempt to execute Romell Broom, a procedure halted by Gov. Ted Strickland in September. Executioners tried for two hours to find a suitable vein for injection, hitting bone and muscle in as many as 18 needle sticks that Broom, 53, said were very painful.

A hearing begins in federal court today on Broom's attempt to stop the state from trying again.

The state had two goals in changing its process. Switching to one drug was meant to end a five-year-old lawsuit that claims Ohio's three-drug system was capable of causing severe pain. Injection experts and defence attorneys agreed a single dose of sodium thiopental would not cause pain.

A backup procedure allowing a two-drug muscle injection was created in case a situation like Broom's execution happened again.

States are watching Ohio's change, but none have made a similar switch. Florida, Kentucky, South Carolina, Texas and Virginia are among those saying they will keep the three-drug method.

It was the second trip to Lucasville for Biros, who spent more than 30 hours in the holding cell in March 2007 before the US Supreme Court stopped his execution and allowed him to make his own challenge to the three-drug method.

US District Judge Gregory Frost refused on Monday to delay the execution, and Biros' appeal was rejected later that night.

Biros argued that the state had failed to fix the problems that led to the unsuccessful execution attempt in September. He said the state still relies on unqualified executioners and lacks limits on how long they are allowed to try to find a vein.

In asking Frost for a stay, Biros had argued that the new execution method still left vein access issues unresolved, subjecting him to the risk of severe pain, and had described the new one-drug approach as "impermissible human experimentation". The judge, in his ruling, called the arguments "unpersuasive".

Frost did say Ohio's execution system still has flaws that "raise profound concerns and present unnecessary risks". He also said he was concerned about the competency of Ohio's executioners and how much they appeared able to deviate from the state's written execution rules.

All 36 death penalty states use lethal injection, and 35 rely on the three-drug method. Nebraska, which recently adopted injection over electrocution, has proposed the three-drug method but hasn't finalised the process.

Biros killed the 22-year-old Engstrom near Warren in 1991 after offering to drive her home from a bar, then scattered her body parts in Ohio and Pennsylvania. Before dying yesterday, he apologised for his crime and thanked his friends and relatives for supporting him.

"I'm being paroled to my father in heaven," Biros said. "I will now spend all of my holidays with my Lord and saviour, Jesus Christ."