An Oklahoma man convicted of murdering a woman during a house robbery was executed on Thursday by lethal injection, marking the third execution in the United States this week.

Wendell Grissom, 56, was sentenced to death for the 2005 murder of Amber Matthews, 23, who was shot in the head while attempting to defend a friend's two small girls.

Grissom was declared dead 10 minutes after the execution began at the state prison in McAlester, according to a statement from the Oklahoma Department of Corrections.

It stated that the execution was carried out using a three-drug protocol: midazolam, which produces sleepiness; vecuronium bromide, which stops respiration; and potassium chloride, which stops the heart.

According to court records, Grissom, a truck driver, and Jessie Johns broke into the home of Dreu Kopf, a friend of Matthews, to commit robbery.

Grissom shot and wounded Kopf and killed Matthews while she was hiding in a bedroom in an attempt to shield Kopf's two children.

Johns received a life sentence with no chance of parole. The execution is the third this week in the country, with a fourth slated for later Thursday in Florida.

Edward James, 63, will be executed by lethal injection for the 1993 rape and murder of Toni Neuner, an eight-year-old child, and her grandmother, Betty Dick, 58.

A death row inmate in the US state of Louisiana was executed on Tuesday using nitrogen inhalation, a method previously employed only in neighboring Alabama and condemned by UN experts as a form of torture.

The execution of 46-year-old Jessie Hoffman, convicted of kidnapping, raping, and murdering Mary "Molly" Elliot in 1996, marked Louisiana’s first execution in 15 years.  

Only one other US state, Alabama, has used nitrogen hypoxia to execute prisoners, which entails pumping nitrogen gas into a facemask and forcing them to suffocate, something UN experts have blasted as brutal and inhumane. 

Aaron Gunches, 53, who had been sentenced for the 2002 murder of Ted Price, his girlfriend's ex-husband, was put to death in Arizona on Wednesday.

Gunches had given up legal action to stop his death.

Since the Supreme Court reintroduced the capital penalty in 1976, the great majority of US executions have been carried out via lethal injection, with the exception of a man executed by firing squad in South Carolina on March 7.

The world’s first execution by nitrogen inhalation occurred on January 25, 2024, in Alabama with the execution of Kenneth Smith, sparking widespread condemnation. Three more executions have since been carried out in the state.  

The death penalty has been abolished in 23 of the 50 US states, while six others—Arizona, California, Ohio, Oregon, Pennsylvania, and Tennessee—have imposed moratoriums on executions.

President Donald Trump supports the punishment and on his first day in office, advocated for an extension of its usage "for the vilest crimes."