The case was as cold as the Michigan winter: Who killed Janna Kelly? Who dumped her body in a field and set it on fire? Why would anyone want the 60-year-old grandmother dead?

Janna's daughter Dana Isola and niece Jennifer Stanton have been desperate for answers ever since Janna vanished.

Eight years ago Janna, a Grand Rapids, Michigan, insurance agent and landlord left work and was never seen again.

The next day Janna's coat and purse were found at a car wash. The following day they found her car abandoned at a Grand Rapids intersection. There was blood on her coat and in the car, but it was never tested for DNA.

The following spring, three and a half months after she disappeared, a land surveyor stumbled upon Janna's remains in a field 40 miles away.

The seasons change, the years pass, the case remained unsolved.

Then, last December, cold-case detectives from the Ottawa County Sheriff's Department reopen their investigation.

One possible clue: Janna's neighbor, Daniel Olson, says she was complaining about one of her tenants. Her name is Robin Root, and Janna evicted her and in a civil action sued the tenant for back rent.

Olson claims he saw Root show up Janna's door two days before she disappeared.

Cops spoke to Root after Janna disappeared. She admitted talking to her, but denied any involvement in her disappearance.

And they even took a DNA sample. That DNA would prove to be the key that would open the door to the cold-case file and finally close it.

Root's DNA sample sat in an evidence locker for seven years and was never sent to a lab to see if it matched the blood found in Janna's car.

The Grand Rapids Police Department admits it was a colossal mess-up.

The DNA was a match.

Detectives found cellphone evidence showing both Root's and Janna's cellphones "pinged" the same towers, starting in Grand Rapids and ending in the field where the body was dumped.

Cops interrogated Root and she caved, admitting to a brutal and horrible killing.

Root said she put Janna in the trunk, still alive and breathing. The temperature plunged to 19 degrees overnight. The next morning Janna was dead.

Root says she took the body to the field and burned the body.

With Root's confession on the record, the main question to be answered at her trial: Was this a premeditated murder?

"Robin Root did not intend to kill Janna Kelly," said Root's attorney, David Dodge. "Robin Root had no motive."

Root was convicted of first-degree murder. She was scheduled to be sentenced in the second week of December, and could face life in prison.