Triple murderer put to death in Texas

File picture shows the Polunsky Unit, where death row inmates are held, in Livingston, Texas, about 40 miles from Huntsville (AFP Photo/Chantal Valery) (AFP/File)

Washington (AFP) - The state of Texas executed a man convicted in the triple murder of his girlfriend, her mother and her grandfather, officials said.

Derrick Charles, 32, was put to death by lethal injection at the state penitentiary in Huntsville at 6:36 pm (2236 GMT), according to spokesman Jason Clark.

His last words before being injected with the lethal drugs were "I'm ready to go home," Clark said.

The US Supreme Court earlier on Tuesday denied a last minute appeal by the condemned man, allowing the execution to proceed.

Charles was just 19 at the time of the murders, which anti-death penalty activists had hoped would be taken into account in appeals that sought to spare his life at trial.

His attorneys also argued in vain that a family history of mental illness should have been taken into account.

Charles' execution comes as a growing number of Americans say they opposed capital punishment, and with an increasing number of US states making the decision to end the practice.

Meanwhile, the US Supreme Court is due next month to rule on the constitutionality of lethal injection -- the most common form of execution in the United States, but one that has become increasingly controversial.

In 2008, the court ruled that lethal injection was constitutional, but that was before recent shortages in the most commonly used drugs prompted state officials to come up with lethal medication cocktails that appeared to cause pain and suffering in inmates during some recent executions.

The execution was the seventh this year in Texas, the US state that has killed more Death Row inmates than any other.

It was the 14th execution this year in the United States.