A deranged Minnesota man allegedly bludgeoned his female co-worker to death with a sledgehammer — and told police he had been plotting the ruthless attack for some time.

David Bruce Delong, 40, was arrested and charged with second-degree intentional murder after repeatedly clubbing 20-year-old Amber Czech with the mallet at Advanced Process Technologies in Cokato around 6 a.m. Monday, according to the Wright County Attorney’s Office and local reports.

Police said the alleged unhinged attacker was captured on surveillance footage leaving his workstation inside the food and dairy machinery plant and approaching Czech before grabbing her sledgehammer and bashing her in the head.

The unsuspecting victim, reportedly a welder, fell to the cement floor as Delong forcefully struck her four more times, according to court documents.

“I hit her with your hammer, she is by your toolbox, she is gone,” the accused killer coldly told another employee afterward.

Authorities found the bloody weapon next to Czech, who died at the scene from blunt force trauma and blood loss, police said.

“The defendant admitted not liking the victim,” authorities said in the documents.

“The defendant said he has been planning to kill the victim for some time.”

Czech, of Hutchinson, was remembered by her grieving father as an outgoing and hardworking young woman who always helped others and took pride in her work as a welder, KARE 11 reported.

She developed a passion for welding in high school and went on to attend Alexandria Technical & Community College, graduating in 2024 after completing a 10-month welding technology program.

Advanced Process Technologies told the outlet that production will remain paused for the remainder of the week, with administrative staff working remotely while police continue their investigation.

“As some in our community know, one of our facilities was the site of a tragic event that resulted in the death of one of our coworkers,” the manufacturer said in a statement on Facebook Wednesday.

“Our hearts are with their family, friends and all who are grieving this loss. We are working closely with law enforcement as they investigate this event and focused on supporting our employees and the victim’s family. Thank you for the messages and comments of support.”

Wright County Attorney Brian Lutes said he plans to present an upgraded first-degree premeditated murder charge to a convening grand jury.

Delong is currently in custody and reportedly due back in court on Nov. 24.