Attorneys for a Nicaraguan man set to be executed for fatally shooting a Houston high school teacher during a robbery more than 18 years ago are contending the man is mentally incompetent to be put to death.

Bernardo Tercero is facing lethal injection Wednesday for the March 1997 shooting of 38-year-old Robert Berger, who was killed as he and his 3-year-old daughter were in a dry cleaners that Tercero came into to rob.

Tercero's lawyers say in a federal appeal his mental incompetence should disqualify him from execution. State attorneys oppose any delay and say he discussed the case clearly in a TV interview.

Prosecutors say the 39-year-old Tercero was in the U.S. illegally at the time of the shooting. He'd be the 11th inmate executed in Texas this year.