MINNEAPOLIS (WCCO) –An 18-year-old Willmar man has been sentenced for his involvement in the murder and robbery plot of his grandmother.

On Wednesday morning, Robert Inocencio Warwick pleaded guilty to first-degree murder while committing a felony and was sentenced to life in prison. Another charge, first-degree premeditated murder, was dismissed.

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Sheriff’s deputies found Lila Warwick dead in her home in Willmar in late July 2013. Investigators said she’d been strangled and stabbed.

Two days later, authorities arrested 19-year-old Brok Junkermeier and 16-year-old Devon Jenkins. The day after that, police arrested Warwick’s grandson, Robert, who was 17 years old at the time.

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Authorities said Robert Warwick put together the plan to rob and kill his grandmother.

The criminal complaint states Junkermeier broke into her home while Jenkins waited in the car. It details Junkermeier admitting to a friend that he cut Warwick with a sword-like knife and forced her to access her bank account on a computer. It also states he made her write out a $1,500 check.

It states Junkermeier strangled Warwick, repeatedly stabbed her, and threw her body in the basement.

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Jenkins has since pleaded guilty to second-degree murder without intent. In April, Junkermeier was sentenced to life in prison.