Warner Lockett
Death row inmates Clayton Lockett (l) and Charles Warner were both executed using a controversial drugs cocktail including the sedative midazolamREUTERS/Oklahoma Department of Corrections

Oklahoma Senators have voted to back a bid to build a gas chamber to execute people on Death Row in the state. The Senate Judiciary Committee voted 9-0 to authorise a bill which would allow the use of "nitrogen hypoxia" to end peoples' lives.

The proposal comes following several recent botched executions including those of Clayton Lockett who was given a cocktail of drugs and was seen to writhe in pain for 40 minutes.

Fellow murderer Charles Warner said his body was "on fire" after being given the same combination of drugs (midazolam, vecuronium bromide and potassium chloride) last month. It is not known how long he suffered as he was also given a sedative which rendered him immobile.

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Capital punishment is legal in 32 US statesREUTERS/Jenevieve Robbins

Nitrogen gas is believed to be a more humane method of execution. The condemned convict's blood is "starved" of oxygen, as happens to scuba divers or pilots at high altitude.

"The death penalty is a just and appropriate punishment for our worst criminals," said Republican state Senator Anthony Sykes who authored the bill, "and nitrogen hypoxia is recognised as one of the most humane methods for carrying out the sentence."

Planned executions of three Oklahoma prisoners are on hold while the US Supreme Court looks into the current method of execution. If the Court rules lethal injection is unconstitutional, Oklahoma may revert to the electric chair and firing squad.

It is becoming so hard for the 32 states which retain the death penalty to procure drugs that Tennessee has already legalised the electric chair if the drugs cannot be obtained while Utah says it will bring back the firing squad.

If the Oklahoma bill is approved a new gas chamber would be constructed at the State Penitentiary costing $300,000 (£200,000). However Sykes concedes his bill will undergo changes before the session ends in May.

Although four other US States theoretically allow execution by poison gases, the last person executed under the method was Walter LaGrand, executed by cyanide gas in 1999 in Arizona.