WILLMAR — A Willmar teenager accused of planning his grandmother’s killing has reached a plea deal, his attorney said Thursday.

Robert Warwick, 18, will plead guilty at a hearing next week to first-degree murder while committing a felony, defense attorney Daniel Mohs said. The other charge — first-degree premeditated murder — will be dropped, Mohs said.

Warwick’s jury trial was set to start July 21. A notice of the Wednesday morning plea hearing was filed Thursday in Kandiyohi County District Court but does not give details.

A spokesman for the Minnesota attorney general’s office, which is helping prosecute the case, referred questions to the Kandiyohi County Attorney’s Office, which did not immediately return a phone call left after hours Thursday.

The plea offers Warwick the possibility of parole after 30 years, Mohs said. It also avoids a trial that would have been painful for Warwick’s family, he said.

“I don’t think he wanted to go in there and have to testify,” Mohs said.

Prosecutors said Warwick hatched the plan to rob and murder his grandmother, 79-year-old church volunteer Lila Warwick, in her Willmar home last summer.

Robert Warwick’s friend, Brok Junkermeier, now 20, pleaded guilty at his trial in April to killing the woman and was sentenced to life in prison without parole.

Junkermeier testified that he and “Robbie” Warwick, who was 17 at the time, had been planning the July ambush robbery and attack for months. In the hours after Lila Warwick’s slaying, the pair returned to her home and stole her safe, which they expected to contain tens of thousands of dollars, Junkermeier told investigators.

A third teen pleaded guilty in December for acting as a lookout.