(CNN) Missouri prison officials executed convicted murderer Russell Bucklew by lethal injection Tuesday night despite objections from activists who thought the method would lead to a gruesome death, CNN affiliate KFVS reported.

Bucklew, 51, was convicted of first-degree murder, kidnapping and first-degree burglary in 1997. He was pronounced dead at 6:23 p.m. CT (7:23 p.m. ET), KFVS said.

Former Cape Girardeau County Prosecutor Morley Swingle, who tried Bucklew, said the death "was very peaceful."

A KFVS reporter who witnessed the execution said she could see Bucklew on a gurney with a white sheet up to his chest. Bucklew was looking away from the viewing room. She said he turned his head so that he was looking straight ahead and was twitching his feet. The he let out a sigh, and there was no more movement. The curtains were closed for a few minutes, she said, and reopened with him still on the gurney.

There were no visible complications, she said. Swingle said Bucklew "closed his eyes and went to sleep."

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