A Texas man on death row for killing a worker who was on his property looking for city code violations was put to death Tuesday.

Adam Ward was given a lethal injection for shooting and killing Michael Walker, a code enforcement officer who was taking photos of junk piled outside the Ward family home in Commerce, about 65 miles northeast of Dallas.

Ward insisted the 2005 shooting was in self-defense, but the 44-year-old Walker only had a camera and a cellphone.

Ward's attorneys, both at his trial and later for his appeals, described him as delusional and mentally ill. Hours before his execution, the U.S. Supreme Court rejected an appeal that argued his mental illness should have disqualified him from the death penalty.

The 33-year-old Ward thanked his supporters, expressed love for his parents who did not attend the execution and said he hoped "some positive change can come from this."

But he insisted the shooting was not a capital murder case.

"This is wrong what's happening," he said. "A lot of injustice is happening in all this. I'm sorry things didn't work out. May God forgive us all."

He was given a lethal dose of pentobarbital and as it took effect, he took a deep breath followed by a smaller one. He then stopped moving.

He was pronounced dead at 6:34 p.m. CDT — 12 minutes after the drug started to flow into him.

Ward became the ninth convicted killer executed this year nationally and the fifth in Texas, which carries out capital punishment more than any other state.

In their appeal to the Supreme Court, Ward's attorneys argued the high court's ban on executing mentally impaired prisoners should be extended to include inmates like Ward who have a severe mental illness and that putting him to death would be unconstitutional because of evolving sentiment against executing the mentally ill.

The justices have ruled mentally impaired people, generally those with an IQ below 70, may not be executed. However, the court has said mentally ill prisoners may be executed if they understand they are about to be put to death and why they face the punishment.