WILLMAR, Minn.-- Brok Junkermeier, the 19-year-old who in the midst of his trial last week surprised even his attorney by pleading guilty to killing his friend's grandmother, Lila Warwick, was sentenced to life in prison without parole Wednesday morning.

As members of two families -- Warwick's and his own -- quietly cried, Junkermeier apologized in Kandiyohi County District Court on Wednesday for the July ambush robbery and attack on Warwick.

"I am so sorry," he said, after taking off his glasses to wipe away tears. "If I could trade my life for hers, I would.

"I pray for their forgiveness," he added, referring to the families. "I’m learning to accept my punishment."

Last week, Junkermeier abruptly changed his plea, admitting on the stand to killing Warwick and saying that he planned the crime with Warwick's grandson, Robert Inocencio Warwick, 18, whose trial has not yet been set.

Two of Lila Warwick's granddaughters made statements at Wednesday's sentencing. Katie Ekbom, 22, said that at first, she was furious about the way her grandmother had died.

"But then it hit me," she said. "Is this how my grandma would want me to live?"

Their mother, Cheri Ekbom, also spoke, occasionally looking at Junkermeier. She said, in part:

The battle of hatred versus mercy is one that has played out often in my mind the last ten days. Hatred and revenge come easily, and I tell myself I am justified in doing so. Since my mom's death eight months ago, I have had a compass to guide me. Quite simply, it's been a compass to honor her. Despite every graphic and appalling word I've heard and witnessed, I do not hate. Returning hatred for hatred and evil for evil: She would not, nor will I. In this, I will honor her.

One morning in late July, Junkermeier sneaked into Lila Warwick’s garage with a long dagger, cutting her hands before forcing her to write him a check for $1,500. He detailed how he stabbed and strangled her in an interview with investigators two days after her body was found on the basement floor.

Junkermeier and “Robbie” Warwick had expected to find tens of thousands of dollars in the safe they picked up on a trip back to her home a few hours after her slaying.

But when the pair pried open that safe, “there was just, like, documents,” Junkermeier said in the videotaped interview, including a high school diploma, passport and baptism certificate. They also took $30,000 in savings bonds in the name of Lila Warwick, which deputies later spotted on Junkermeier’s bedside table.