GRAND RAPIDS, Mich. (WOOD) — Whoever fatally stabbed Renee Pagel on Aug. 5, 2006, planned the murder carefully.

Investigators with the Kent County Sheriff’s Department say the killer left behind virtually no physical evidence.

As a result, 13 years later, Kent County Prosecutor Chris Becker says detectives are “nowhere close” to making an arrest in the murder of the 41-year-old mom and teacher.

That’s even though detectives developed a prime suspect early on: Renee’s estranged husband, Mike Pagel.

“It’s a difficult case,” said Becker.

“There’s not a whole lot there right now in terms of evidence. We are fully aware of it. We have not forgotten about it by any stretch of the imagination. It’s not sitting in a box somewhere,” he added.

In fact, a cold case review team made up of Michigan prosecutors met in Lansing last fall to review the case file.

“The cold case team gave us some ideas to follow up, and the sheriff’s department is working on it,” said Becker.

Renee’s friend, Chris Crandle, continues to speak out to ensure no one forgets the generous woman who even donated a kidney to a student’s father.

Pagel was recovering from the surgery the night someone stabbed her to death in her bed in the Rockford home she once shared with her husband and three children.

“She gave and gave and gave,” said Crandle. “Her last act was giving an actual piece of herself — her kidney — to someone she never even knew. Who does that?”

Sgt. Bill Marks of the Kent County Sheriff’s Office said investigators determined the murder happened overnight.

“There were defensive wounds. There was evidence that this occurred over a period of time – more than just a matter of seconds — and that there was active resistance,” said Marks.

Crandle has been vocal about her belief that Renee’s estranged husband —Mike Pagel — killed her.

“She told me every day of that last week of her life she thought he would kill her. She was afraid,” recalled Crandle.

The Pagels were going through a highly contentious divorce that was nearly finalized when the murder happened. Renee Pagel was set to get the house and primary physical custody of the couple’s three children.

But Mike Pagel’s attorney, Frank Stanley, said his client did not kill Renee Pagel.

“He did not do it. The police know he didn’t do it,” said Stanley. “That’s why he’s not charged. There’s no physical evidence. He has an alibi. There wasn’t enough time for him to commit this crime.”

Mike Pagel has said he was with his children at his mother’s house when Renee was killed.

Chris Crandle, who put up billboards and created a website to keep the case in the public eye, doesn’t buy it.

“If he’s innocent, why has he not ever come and tried to clear his name?” Crandle asked.

Marks said those involved in the case have cooperated with the police investigation, with the exception of Mike Pagel.

“I would say he’s evasive. He was certainly not forthcoming and not overly concerned with calling and helping us solve this case,” said Marks.

Mike Pagel lives near Saginaw now. The couple’s three children are now in their late teens and early twenties.

“What has been done to let them know who their mom really was?” Chris Crandle wondered. “She was the most generous person that I ever knew.”