"Over time lethal injection has become only more problematic and chaotic,” Deborah W. Denno, a professor at Fordham Law School, told the New York Times, summarizing the ongoing battles that have led states to adopt new drug sources or alternative methods of execution. Several states have obtained or sought drugs using sources that may violate pharmaceutical regulations. For the execution of Alfredo Prieto, Virginia obtained pentobarbital from the Texas Department of Criminal Justice, which purchased it from a compounding pharmacy whose identity is shielded by the state's secrecy law. "Even if the transactions between states do not comply with law, there is no recourse for death-sentenced prisoners," said Megan McCracken, an expert in lethal injection at the Death Penalty Clinic at the University of California, Berkeley, School of Law. Both Nebraska and Ohio received warnings from the Food and Drug Administration that their attempts to purchase sodium thiopental from overseas suppliers violated federal law regarding the importation of drugs. Oklahoma executed Charles Warner in violation of its own execution protocol, substituting an unauthorized chemical, potassium acetate, for the potassium chloride its regulations require. Other states have turned to alternative execution methods: Tennessee reauthorized use of the electric chair, while Oklahoma passed a bill to make nitrogen gas asphyxiation its backup method. Louisiana prison officials also recommended using nitrogen gas, but the state has not taken action on that recommendation. The scramble for lethal injection drugs has delayed executions across the country. A challenge to Mississippi's protocol has halted executions until at least next year. A Montana judge put executions on hold because the state's proposed drug cocktail violated state law, and either the drugs that comply with state law are not produced in the U.S. and may not be imported or the manufacturer refuses to sell the drug for executions. In Oklahoma, the Attorney General requested an indefinite hold in order to review lethal injection procedures after the state obtained the wrong drug for the execution of Richard Glossip.