The U.S. Supreme Court was considering whether a Texas man who killed a city worker in 2005 should be spared from a lethal injection, as his lawyers argue that a ban on executing mentally impaired prisoners should be extended to him.

Adam Ward's attorneys say he's delusional and should not be put to death because of his mental illness. His execution is set for Tuesday evening and would be the fifth this year in Texas and ninth nationally.

Ward, 33, insists he was defending himself when he killed code enforcement officer Michael Walker, who was taking photos of junk piled outside the Ward family home in Commerce, about 65 miles northeast of Dallas.

"Only time any shots were fired on my behalf was when I was matching force with force," Ward told The Associated Press last month from a visiting cage outside death row. "I wish it never happened but it did, and I have to live with what it is."

Evidence showed the 44-year-old Walker had a camera and cellphone but no weapon.

In a videotaped statement to police following his arrest, Ward said he believed Commerce officials long conspired against him and his father, described in court filings as a hoarder who had been in conflict with the city for years. Evidence showed the Ward family had been cited repeatedly for violating housing and zoning codes.