FLORENCE, Ariz. -- The attorney for an Arizona death-row inmate executed Wednesday said he was "very disturbed" after seeing his client shake for several seconds upon receiving his lethal injection, and he wants to find out if the man felt any unnecessary pain.
Thomas Arnold Kemp, 63, was executed at the state prison in Florence for killing a Tucson college student after robbing him of $200 in July 1992.
Kemp lay strapped to a table in the death chamber as he delivered his final words: "I regret nothing." He then nodded and smiled at his attorney, Tim Gabrielsen, looked at the ceiling and calmly waited.
As the one-drug execution began, Kemp's eyes closed and his body visibly shook for several seconds before he went quiet and appeared to fall asleep with a few deep breaths. His time of death was 10:08 a.m.
Gabrielsen later told The Associated Press he was concerned about his client's shaking and was considering what action could be taken to determine if Kemp experienced pain, including an autopsy by an independent pathologist.
"It was unmistakable," said Gabrielsen, who has witnessed one other execution. "He was shaking very violently. We're very disturbed by that."
In the past nine Arizona executions attended by the AP since 2007, no other inmates shook as they were given a lethal injection.
State Department of Corrections spokesman Bill Lamoreaux said Kemp was offered a mild sedative before the execution but turned it down.
"Also, the air conditioner was on and he expressed he was a little chilly," Lamoreaux said in an email to the AP. "The air conditioner was turned off, and (Corrections Director Charles Ryan) personally directed the inmate be covered with a couple of blankets."
All inmates executed in Arizona are offered a sedative, but the vast majority decline it.
Kemp was executed using one drug, pentobarbital. Most states use a three-drug process and "the second drug would mask any movement or pain," said Richard Deiter, executive director of the Death Penalty Information Center in Washington, D.C.
Deiter said it's hard to know if Kemp "had a strong adverse reaction" to the pentobarbital.
"Sometimes it depends on the individual," he said. "Maybe he had an unknown (medical) problem."
Jonathan Groner, an Ohio State University surgeon who has studied lethal injection extensively, said high doses of pentobarbital are associated with seizures, and that may have caused Kemp's shaking.
"The problem is the people that give it are not physicians. They try to push it as fast as possible," Groner said. "It's nothing anyone would do in a hospital or medical center. It's not a very good way to kill people."
Kemp was sentenced to death for kidnapping Hector Soto Juarez from outside Juarez's Tucson home on July 11, 1992, and robbing him before taking him into the desert near Marana, forcing him to undress and shooting him twice in the head.
Juarez, 25, had just left his apartment and fiancée to get food when Kemp and Jeffery Logan spotted him. They held him at gunpoint and used his debit card to withdraw $200 before driving him to the Silverbell Mine area, where Kemp killed Juarez.
The two men then went to Flagstaff, where they kidnapped a married couple traveling from California to Kansas and made them drive to Durango, Colo., where Kemp raped the man in a hotel room. Later, Kemp and Logan forced the couple to drive to Denver, where the couple escaped. Logan soon after separated from Kemp and called police about Juarez's murder.
Logan led police to Juarez's body, and Kemp was arrested. Logan was later sentenced to life in prison.
With three lethal injections already this year, Arizona could match its record year for executions.
Arizona executed Robert Henry Moormann on Feb. 29 and Robert Charles Towery on March 8. Another inmate, Samuel Villegas Lopez, is scheduled to be executed May 16 for the brutal rape and murder of a Phoenix woman.
Three other inmates who are near the end of their appeals also could be put to death this year, putting the state on pace to execute seven men in 2012.
Arizona established its death penalty in 1910. Since then, the most inmates Arizona has executed in a given year was seven in 1999.
Associated Press Writer Walter Berry contributed to this report.