Two weeks ago, the Texas Department of Criminal Justice obtained a new supply of pentobarbital, a drug commonly used in capital punishment. But where, precisely, the drugs came from is anybody’s guess.

As the Associated Press reports, Texas officials “cited unspecified security concerns in refusing to disclose the source and other details about the sedative it plans to use to put inmates to death.” On Tuesday, an assistant general counsel with the Texas prison system cited a bomb threat against a supplier in a brief as reason not to disclose the supplier of execution drugs.

Texas found its new supplier of dubious drugs after its previous supplier, a compounding pharmacy in suburban Houston, refused to sell more pentobarbital to the state after its name was made public.

Last week, prompted by lawyers for two death row inmates who argued that the prisoners have a right to know the details of their execution, a judge ordered officials to release information on the execution drugs. The state is in the process of appealing that ruling.