A Texas man convicted of killing a convenience store clerk in 2000 is set to be executed by lethal injection on Wednesday. If carried out, it would be the 30th execution in the US this year.Jamaal Howard, 46, was convicted of capital murder in the killing of Vickie Swartout, 42. She was shot once in the chest during a robbery at a store in Silsbee, a small town about 161 km northeast of Houston.Howard was 20 when the killing took place. According to court records cited by news agency Associated Press, he took $114 and a carton of cigarettes from the store. Surveillance video presented during the trial showed Howard shooting Swartout.Howard’s lawyers have argued that he is intellectually disabled and should not be executed. The state has argued that he has not provided enough evidence to support the claim.Howard has also asked the US Supreme Court to stop the execution.The Supreme Court barred the execution of people with intellectual disabilities in 2002, but allowed states some discretion in deciding whether a person meets the criteria.If Howard’s execution goes ahead, he will be the seventh person executed in Texas this year. Two more executions are currently scheduled in the state.The execution would come after a failed attempt last week to execute Christa Pike in Tennessee. Pike’s lawyers said on Tuesday that she remained awake and was speaking while receiving treatment at a hospital.