(Reuters) - Lawyers for a convicted killer are calling for an investigation into his Wednesday night execution in Virginia, saying a delay in the process suggested he underwent "pain and suffering inconsistent with his constitutional rights."


Ricky Gray, 39, died by lethal injection at 9:42 p.m. at Greensville Correctional Center.


He had been sentenced to death for the 2006 slayings of sisters Ruby Harvey, 4, and Stella Harvey, 9. He also killed their parents and confessed to participating in the murder of another family days later.


His attorneys said in a statement that a curtain that kept Gray from view while corrections employees inserted an intravenous line remained closed for more than 30 minutes, far longer than usual.


Gray gasped and snored after the first of three drugs, a sedative known as midazolam, was administered. That drug had not previously been used by Virginia in executions. The noises could have been a sign that Gray was still conscious and could feel pain, his lawyer said.


The attorneys said that in addition a doctor emerged from behind the curtain to check Gray's heart after the injections. The normal protocol calls for the doctor to remain hidden and determine the time of death based on a heart monitor.

A spokeswoman for the state department of corrections, Lisa Kinney, said in an email that the initial delay occurred because it took staff time to find a vein for IV insertion, a process the department follows "with the utmost care." She said Gray did not react to a stimuli test after the sedative was administered, contrary to his attorneys' statement.

Critics have said that midazolam had failed to render inmates unconscious properly during executions in other states, causing them unnecessary pain.

In October, a man executed by Alabama heaved and coughed for 13 minutes before dying, and critics of capital punishment said his reaction was caused by midazolam. They have said the drug should be banned because it does not render a prisoner sufficiently unconscious.

Gray's attorneys unsuccessfully tried to have his execution stayed by the U.S. Supreme Court on Wednesday, arguing in part that the midazolam used in Virginia was riskier because it came from a compounding pharmacy, not a drug manufacturer.

Gray was the second inmate to be executed in the United States this year.

(Reporting by Joseph Ax; Editing by Toni Reinhold)