WILLMAR, Minn. – In the slaying of Willmar grandmother Lila Warwick, prosecutors say the teenagers played three distinct roles: the mastermind, the lookout and the killer.

The mastermind was allegedly Warwick's own grandson, Robert Inocencio Warwick. The lookout pleaded guilty, apologized and was sentenced in juvenile court. This week, Brok Junkermeier — the 19-year-old who stabbed and strangled Warwick — goes to trial. Jury selection begins Tuesday.

"This isn't a whodunit case," said his attorney Kent Marshall. "We know who killed Lila Warwick. The issue for the jury is not whether he committed murder, but what degree of murder they should convict him of."

Junkermeier has pleaded not guilty to first-degree murder charges for allegedly carrying out the July ambush robbery and attack that he and Warwick, who was 17 at the time, had been planning since December 2012. Whether prosecutors can prove such premeditation could be key to a first-degree conviction.

Evidence presented in the Kandiyohi County Courthouse could also preview Robert Warwick's trial, not yet scheduled, and reveal why the teenagers targeted Lila Warwick, 79, whom family, neighbors and fellow churchgoers have remembered as a doting grandmother and devoted volunteer.

The homicide shocked Willmar, a west-central Minnesota city of about 19,500, and a grieving family suddenly was forced to confront the fact that "Robbie" was allegedly involved.

Flowers were placed outside the Willmar home of Lila Warwick, 79, in August.

"We are trusting that justice will be served in this young man's life," said Cheri Ekbom, Lila Warwick's daughter said of Junkermeier. "I am hoping just to see him have to pay, to pay with time behind bars for ­taking my mom's life."

Eight months after her mother's death, Ekbom misses chatting with her when ­driving home from work or walking the dog.

"It's such a little thing," she said, "but I miss calling and talking to her."

The gruesome crime

Junkermeier and Robert Warwick, now 18, "believed there was a lot of money" in Lila Warwick's safe, according to a March memo from prosecutors. That document says that a "close friend" witnessed their planning and could testify in the coming trial.

"Brok Junkermeier stated that he would kill Lila Warwick so there would not be a witness," the memo says. "Robert Warwick was OK with Brok Junkermeier making the ­decision of whether or not to kill Lila Warwick."

Warwick allegedly told Junkermeier about his grandmother's house and habits — including where she hid a spare key.

Very early on a morning in late July, Junkermeier waited in the garage for more than two hours until Lila Warwick entered. He confronted her with a 20-inch knife described in court documents as both a sword and a dagger. Then he cut her hands, prosecutors say, and demanded she write him a check for $1,500 before bringing her to the basement. There, he allegedly strangled and stabbed her.

After a four-hour, recorded interview with detectives, Junkermeier took them to where he had discarded the knife and his bloodied clothing, according to court documents.

By phone last week, Marshall pledged to represent Junkermeier "zealously" but declined to preview his ­strategy. Months ago, Marshall requested that Junkermeier receive a mental competency examination, the results of which are private.

But "there will be no mental illness defense in this case," he said last week.

"It's a horrible crime. I'm sure it shocks the conscience of the people of Kandiyohi County," Marshall said. "But despite that, Brok Junkermeier is, in many ways, a very good kid.

"Sometimes good people do really bad things."

Grandson the mastermind?'

When people learn that attorney Daniel Mohs is representing Robert Warwick, "the first thing that comes out of their mouths is, 'Oh, you've got the organizer, the mastermind, you've got the planner," he said.

But he pushes back. Robert Warwick might have plotted to burglarize his grandmother's house and steal her money, Mohs said in an interview. "But I don't think there was a plot to intentionally kill her."

Instead, Mohs suggested that Junkermeier surprised the others by killing Lila Warwick, who was 5-foot-3 and 110 pounds. Marshall declined to comment on that idea.

The 16-year-old "lookout," Devon James Jenkins, pleaded guilty in January to one count of unintentional second-degree murder. His sentence included a pair of correctional programs, 100 hours of community service annually and probation until age 21, according to court records.

Robert I. Warwick

Jenkins is expected to testify at Junkermeier's trial, as is Robert Warwick. The prosecution lists four dozen possible witnesses, including neighbors, teenage friends and detectives.

Evidence includes a pair of handcuffs, autopsy photos, cellphone records and surveillance video from Bremer Bank of Junkermeier cashing the check Lila Warwick had written him.

Ekbom, of Brooklyn Park, plans to attend the trial, despite trepidation about seeing "pictures of my mom that no person should have to see of a person who they love."

Although they want Junkermeier to "pay the price," Lila Warwick's relatives "are not vengeful, hateful people," Ekbom said. "My mom wasn't like that … and I am so mindful of doing the honorable thing for her.

"I hate evil," Ekbom said. "But I don't hate this person."

Jenna Ross • 612-673-7168