A convicted serial killer was executed in Texas on Thursday by a lethal injection that came from an undisclosed source. The Supreme Court declined to halt the execution of Tommy Lynn Sells, 49, despite his lawyer’s plea that too much secrecy surrounded the source of pentobarbital. The Supreme Court sided with Texas prison officials, who argued that the source had to remain a secret to protect the supplier from threats of violence. The issue of secrecy surrounding pentobarbital sources for lethal injections has come up more frequently, as drugmakers increasingly refused to sell it in cases of capital punishment. So far, the Supreme Court has rejected stays on the basis of these drug concerns.