LONDON — Europeans largely consider the death penalty a particularly brutal American anachronism, but the prolonged death of Clayton D. Lockett in Oklahoma, after a botched execution by lethal injection, produced more than the usual horror on Wednesday.

The death penalty is banned in the European Union, which has also moved to ban the export of sedatives like sodium thiopental for use in lethal injections. The drug’s producer has stopped making it, and other European companies have sought to prevent their drugs from being used for executions, fearing European Union sanctions. As a result, the authorities in Oklahoma, and officials in other states, have been improvising new mixtures of drugs.

According to the International Commission Against the Death Penalty, based in Switzerland, Belarus is the only European country that still carries out legal executions, usually by a gunshot to the head. But for some Europeans on Wednesday, even that method of killing seemed humane compared with what Mr. Lockett suffered until his heart stopped, about 43 minutes after the process began. Many here agreed with Madeline Cohen, a lawyer who witnessed the execution, who said that Mr. Lockett had been “tortured to death.”