Sean O'Brien, then 18 years old, was one of six members of a Houston, Texas street gang who raped, tortured, and killed Elizabeth Peña, 16, and Jennifer Ertman, 14, on June 24, 1993. The two girls, who attended Waltrip High School, had been attacked as they took a shortcut home along railroad tracks and stumbled upon the gang, who were drinking beer after initiating a new gang member. Their decomposing bodies were found four days later. Shortly before his execution O'Brien also admitted to murdering Patricia Lopez, a 27-year-old mother of three, after attempting to rape her on January 4, 1993. In his confession he implicated Peter Cantu.
O'Brien was due to be executed on May 16, 2006, when his lawyers won a reprieve from the Texas Court of Criminal Appeals the day before the execution was scheduled. Days later, the same court lifted its earlier order and cleared the way for his execution.
On July 11, 2006 his lawyers again tried to get a stay of execution, with an appeal to the U.S. Supreme Court. This was rejected about a half an hour before he was scheduled to die. O'Brien's lawyers had unsuccessfully argued that no legal procedure existed to allow condemned Texas prisoners to raise challenges that drugs used in lethal injections cause "unnecessary, excessive, and excruciating pain".
When asked if he had a final statement, O'Brien raised his head from the death chamber gurney, looked straight at the relatives of the victims, and said:
The lethal injection was started at 6:12 p.m. and O'Brien was pronounced dead at 6:19 p.m.