Tommy Lynn Sells, 49, died Thursday just after 6:30 p.m. in the state prison in Huntsville. He was suspected of about 15 killings and boasted of dozens more.
Sells was sentenced to death in Texas for stabbing Kayleen "Katy" Harris, after invading the 13-year-old's bedroom in Del Rio on New Year's Eve in 1999. He also attacked a friend, who survived and testified against Sells at his trial.
He received a life sentence for kidnapping and killing Mary Bea Perez, 9, in April 1999.
A federal judge in Houston ruled Wednesday that the state must reveal to lawyers for Sells and Ramiro Hernandez-Llanas, who is scheduled to die Wednesday, the pharmacy supplying the pentobarbital used for the executions. Sells was the first to be executed in the state using the powerful sedative.
A federal appeals court lifted the stay later Wednesday, and the U.S. Supreme Court refused Thursday to hear the case.
Sells made no final statement. Relatives of his victims welcomed the execution.
"For me, to see him die, I'm happy," said Joan Torrez, Mary Perez's grandfather. "And other people think its cruelty, but it really isn't. It's payback time, okay? We have all suffered so many years. But we have gone to hell and back."
In a statement while the appeal to the Supreme Court was still pending, lawyers for Sells and Hernandez-Llanas said the state must be open about its execution methods.
"It is our belief that how we choose to execute prisoners reflects on us as a society," the lawyers said. "Without transparency about lethal injections, particularly the source and purity of drugs to be used, it is impossible to ensure that executions are humane and constitutional."