Derrick Sean O'Brien, 31, was executed by lethal injection on 11 July 2006 in Huntsville, Texas for the rape and murder of two teenage girls.
Elizabeth Pena, 16, and Jennifer Ertman, 14, spent the evening of 24 June 1993, at the swimming pool of a friend's apartment complex in Houston. As their midnight curfew approached, they debated the fastest route to Pena's home. They decided to follow the railroad tracks through a city park.
That same evening, eight young men were in the park participating in a gang initiation ritual. Raul Villareal, 17, was being initiated into the Black and White gang. The other gang members present were O'Brien, Peter Cantu, and Jose Medellin - all 18 - Efrain Perez, 17, and Roman Sandoval. Frank Sandoval and Vernancio Medellin, brothers of two of the gang members, were also present. The initiation consisted of Villareal fighting each of the other gang members for several minutes. Following this ritual, they drank beer.
At about 11:30 p.m., the two girls walked by. As they passed, Jose Medellin grabbed Pena and dragged her down a hill. She screamed for help. Ertman tried to help Pena, but Medellin grabbed her and dragged her down the hill as well. The boys then raped both girls for more than an hour before beating and strangling them. Their bodies, which were left in the woods, were discovered four days later, decomposing rapidly in the sweltering Houston summer heat.
News crews came out to cover the story of two bodies being discovered in a Houston park. O'Brien was caught on videotape in the crowd that gathered at the scene of the discovery. He was smiling. He and the other suspects were arrested after police received a tip from a brother of one of the gang members.
At his arrest, O'Brien confessed that he and the other gang members raped both of the girls. He also confessed that he and Jose Medellin strangled Ertman. They wrapped his red nylon belt around her neck, then he pulled at one end while Medellin pulled at the other, until the belt snapped in two. The belt was found in a search of O'Brien's apartment.
The medical examiner testified that, in addition to both girls being raped and strangled, Ertman had three fractured ribs, and Pena had one tooth that was fractured and several that were missing, indicating that she had been punched or kicked in the mouth.
O'Brien had previously been arrested for shoplifting, assault, and stealing a car. A Houston police officer testified that, about three months before the murder, he witnessed O'Brien and Cantu punch, kick and drag a man at a fast food restaurant. Gregory Ristivo testified that he and O'Brien stole between 25 and 50 cars together, and that O'Brien also assaulted people to steal their shoes. Ristivo also testified that O'Brien and Cantu would start fights with random people.
O'Brien's mother and grandfather also testified against him at his punishment hearing, describing him as "cruel" and "intentionally harsh."
O'Brien was also suspected in the murder of Patricia Lopez, who was found stabbed to death in a Houston park on 4 January 1993. Jose Martin Medellin, the brother of Jose and Vernancio Medellin, testified that Cantu told him that O'Brien killed Lopez. O'Brien was present when Cantu made this statement, and agreed with it. O'Brien was also connected to the crime by fingerprints found on beer bottles found at the scene.
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