What Happened Last Night? Questions Remain After Arkansas Execution

Kelly Kissel of the Associated Press describing the inmate's reaction to the controversial lethal injection drug called midazolam.
Credit Sarah Whites-Koditschek / Arkansas Public Media

The execution of inmate Kenneth Williams on Thursday night has prompted calls for an investigation after reports that he was lurching and convulsing about 3 minutes into the lethal injection process.

Williams is the fourth convicted killer put to death in Arkansas over a period of 8 days.

What happened last night, and how is it linked to a controversial drug used in the deadly three-drug cocktail? We'll explain.