Washington, United States (AFP)-A South Carolina man convicted of a 2005 double murder was put to death by lethal injection on Friday, the fourth execution in the United States this week.

Stephen Stanko, 57, was pronounced dead at 6:34 pm (2234 GMT) at the state prison in Columbia, the South Carolina Department of Corrections said in a statement.

Stanko had a choice between his method of execution — firing squad, electric chair or lethal injection.

He chose lethal injection.

Stanko was convicted of the 2005 murders of his girlfriend, Laura Ling, 43, and Henry Turner, a 74-year-old friend.

He also raped Ling’s teenage daughter and slit her throat but she survived and testified against him at trial.

In a final statement read by his attorney, Stanko said he was “truly sorry for the pain and loss that I caused.

“Sorry is never enough but that does not mean it should not be said.”

Stanko was the fourth Death Row inmate executed in the United States this week.

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

John Hanson, 61, was executed by lethal injection in Oklahoma on Thursday for carjacking and kidnapping Mary Bowles, 77, from a mall in the city of Tulsa and then shooting her to death along with a witness, Jerald Thurman.

Hanson had been serving a life sentence for bank robbery in a federal prison in the state of Louisiana but the Trump administration approved his transfer to Oklahoma so he could face the death penalty.

Anthony Wainwright, 54, convicted of the 1994 murder of Carmen Gayheart, 23, a nursing student and mother of two young children, was put to death by lethal injection in Florida on Tuesday.

Gregory Hunt, 65, convicted of the 1988 rape and murder of his girlfriend, Karen Lane, 32, was executed by nitrogen gas in Alabama that same day.

There have been 23 executions in the United States this year: 18 by lethal injection, two by firing squad and three by nitrogen hypoxia, which involves pumping nitrogen gas into a facemask, causing the prisoner to suffocate.

The use of nitrogen gas as an execution method has been denounced by UN experts as cruel and inhumane.

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