Robert James Campbell, 41, was scheduled to die by lethal injection at 6 p.m. for kidnapping, robbing, raping and killing Alexandra Rendon, a young Houston bank teller, in 1991.
Campbell's legal team argues that Texas should delay the execution while investigators determine what went wrong in Oklahoma when Clayton Lockett was put to death April 29. Lockett died of a heart attack 10 minutes after prison officials halted the execution because the drugs being used to kill him did not appear to be working.
The lawyers also say that Campbell has an IQ so low he should be spared the death penalty under a Supreme Court ruling barring the executions of those of sub-standard intelligence. The Association of Retarded Citizens appealed to Gov. Rick Perry in a letter emailed to reporters.
In the letter, the group says new evidence suggests Texas withheld the results of two IQ tests.
"The actions of state officials have created a gross miscarriage of justice regarding counsel's efforts to appeal Mr. Campbell's sentence," the letter said.
In appeals to federal courts, Campbell's lawyers argued that Texas's policy of refusing to disclose the suppliers of execution drugs means he is at risk of an ordeal like Lockett's. Unlike Oklahoma, Texas has a one-drug protocol, using a massive dose of the sedative pentobarbitol.
Texas has held more executions, 515, in the modern era than any other state.