Atmore, Alabama - A man who maintained his innocence after being convicted of murder was executed by nitrogen gas in Alabama on Thursday.

Anthony Boyd (54), who has steadfastly maintained his innocence, was sentenced to death in 1995 for the murder two years earlier of 32-year-old Gregory Huguley.

He was pronounced dead at 6:33 PM Central time at a state prison in the town of Atmore, the state department of corrections announced.

"At 5:50, correctional officers clad in blue, their name tags removed, opened the curtains of the death chamber to begin the state’s grim orchestration. Before those curtains would close about 37 minutes later, Boyd would gasp for air inside the gas mask more than 225 times," eyewitness reporter Lee Hedgepeth described.

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At trial, prosecutors said that Boyd and three other men abducted Huguley at gunpoint because he allegedly failed to pay for $200 of cocaine. Huguley was driven to a baseball field, bound with duct tape, doused with gasoline, and set on fire.

Boyd was convicted largely on the testimony of a co-defendant, Quintay Cox, who was spared the death penalty.

"I didn’t kill anybody. I didn’t participate in killing anybody," Boyd said when asked if he had any final words, according to Hedgepeth. "There is no justice in this state. It’s all political. It’s revenge motivated. It’s not about closure, because closure comes from within, not with an execution."

"There will be no justice in this state until we change this system. I want all my people to keep fighting. Let’s get it."

This was the 40th execution in the US this year, the most since 2012, when 43 people were put to death. Florida has carried out the most executions with 14, followed by Texas and Alabama with five each.

Nitrogen hypoxia, which involves pumping nitrogen gas into a face mask, causes the prisoner to suffocate.

The use of nitrogen gas as a method of capital punishment has been denounced by United Nations experts as cruel and inhumane.

The death penalty has been abolished in 23 of the 50 states, while three others – California, Oregon, and Pennsylvania – have moratoriums in place.

President Donald Trump is a proponent of capital punishment and, on his first day in office, called for an expansion of its use "for the vilest crimes."