Updated — April 29, 11:30 p.m. ET:
An Oklahoma inmate died Tuesday night of a heart attack after the botched delivery of a new lethal drug combination, Oklahoma Department of Corrections Director Robert Patton said.
The execution officially began at 6:23 p.m. CT when officials administered the first drug. A doctor declared Lockett to be unconscious at 6:33 p.m. CT, then officials proceeded to inject the other two drugs into the inmate.
A few minutes later, Lockett, 38, reportedly started moving on the gurney and eventually started shaking uncontrollably. Witnesses reported hearing someone say "something's wrong," although it was not clear who made the statement.
A doctor reportedly lifted the sheet that was covering Lockett to examine the injection site and an official who was inside the death chamber lowered the blinds.
"It's come to my attention, I'm stopping the execution," Patton said to the media in the execution chamber. "We've had a vein failure, in which the chemicals did not make it into the offender."
Lockett died at 7:06 p.m. CT of a heart attack with all three drugs having been administered.
Charles Warner's execution was also set for Tuesday night, but the action was stayed for 14 days after the botched injections.
Lockett, a four-time felon, was convicted of shooting 19-year-old Stephanie Neiman in 1999 and watching as accomplices buried her alive. Warner, 46, was convicted of raping and killing an 11-month-old girl in 1997.
The drug mix set to be used in Lockett's and Warner's executions had never been tried before by the state of Oklahoma, Jerry Massie, public information officer for the state department of corrections, said.
Lockett was first to be injected with midazolam, a benzodiazepine meant to make the inmate unconscious and unable to feel pain. The second injection is of vecuronium bromide, meant to stop breathing, and then potassium chloride, which stops the heart.
The combination has been used previously in Florida, but with a higher dose of the first drug than was used Tuesday in Oklahoma. Without effective sedation, the prisoner may suffer from suffocation and pain.
Drug companies say they do not want their information released because they are fearful of political repercussions and even physical attack, and often refuse to supply drugs, forcing states to scramble to find new sources and try untested combinations.
Others argue not releasing where the drugs come from violates due process and the ban on cruel and unusual punishment, because it is not clear if the drugs are safe and effective. Both inmates had tried to delay the executions citing the secrecy behind where the state acquired the drugs.