Updated

The Latest on the final execution in Arkansas before the state's supply of a lethal injection drug expires at the end of the month (all times local):

6:25 a.m.

The American Civil Liberties Union says Arkansas may have subjected a death row inmate to cruel and unusual punishment in its rush to use a lethal injection drug before it expires, following reports that the man convulsed and lurched during his execution.

Rita Sklar, the executive director of the ACLU of Arkansas, has called for an investigation into witness accounts of Kenneth Williams' execution to "determine whether the state tortured" him.

An Associated Press reporter who witnessed Williams' execution Thursday says his body jerked 15 times in quick succession about three minutes into the process. He lurched violently against the leather chest restraint, then the rate slowed for a final five movements.

Sklar said in a statement Friday that Gov. Asa Hutchinson "ignored the dangers" to beat the Sunday expiration date of the state's supply of midazolam.

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3 a.m.

The last of four Arkansas executions over an eight-day period has prompted calls for investigations after the inmate lurched and convulsed while strapped to the gurney.

An Associated Press reporter who witnessed Kenneth Williams' execution Thursday said that about three minutes into the lethal injection, his body jerked 15 times in quick succession. He lurched violently against the leather chest restraint, then the rate slowed for a final five movements.

One of Williams' attorneys called the execution "horrifying." A spokesman for Gov. Asa Hutchinson called it "an involuntary muscular reaction."

The compressed lethal injection timeline could attract more scrutiny after Williams' death. Arkansas sought to carry out as many lethal injections as possible before one of its drugs expires Sunday. It executed four prisoners, while four others received court stays.