Last February, Natrona County Sheriff's investigator Michael Steinberg asked his supervisor for a cold case to work on.

He was told to look into the death of Tammy Dively, a 25-year-old single mother who had been run over by a vehicle along Hat Six Road, east of Casper.

Steinberg took all of the information on the case home with him and read it for an entire weekend. As he studied the paperwork, a suspect began to emerge.

"When I read through it, all the information pointed to Jeff Smith," he said. "So that is how it got started."

It ended Tuesday with a jury ruling that Smith was a habitual criminal, meaning his second-degree murder conviction, handed down by the same jury a day earlier, will lead to a mandatory life sentence.

The verdict ends an investigation that began 21 years ago along a dirt road in a sparsely populated area of Natrona County.

"We feel we knew for the past year who committed this crime," Steinberg said. "At least (Dively's) family has some answers they didn't have."

A jury of six men and six women agreed with prosecutors that Jeffrey Lynn Smith, 44, ran over Dively with his truck sometime between 6:30 p.m., when she was last seen at her Casper home, and 7:45 p.m., when her body was found.

Smith was interviewed by investigators a day after the killing, but it was only after DNA tests linked Smith to seminal fluid recovered from Dively's body that he was charged with her murder.

Although prosecutors couldn't place Smith at the crime scene, they offered evidence that, a little more than an hour before her body was found, Dively got into an older, blue and white pickup truck matching the description of one owned by the defendant.

Natrona County District Attorney Michael Blonigen also highlighted Smith's inconsistent statements to investigators. Days after the killing, Smith told investigators that Dively had showed up at his house a little after 8 p.m. on the night of her death. Her body had actually been found about 20 minutes earlier.

The jury deliberated less than three hours Monday, and the lead juror said the lack of alternative suspects and evidence in various categories led jurors to side with the prosecution.

Terry Crabb said the jury organized information from the trial into multiple "areas," which they used to determine Smith's fate.

"What it boiled down to was there were seven, eight, nine areas," Crabb said.

Each of those areas - such as DNA tests connecting seminal fluid found inside Dively's body to Smith - were areas "we could not exclude Mr. Smith from," the juror said.

Only the DNA evidence pointed directly to Smith, Crabb said. But other areas of evidence, such as corroborating statements from multiple witnesses, combined with Smith's inconsistent alibi, did not direct blame away from the defendant.

The defense made good points in regards to the difficulty some witnesses had in recollecting events that took place in 1986. Still, Crabb said the evidence showed him that only one person could have killed Dively. The rest of the jury agreed.

Dively's daughter, now known as Stephanie Zouari, impressed Crabb. She testified last week that, as a 7-year-old, she saw her mother walking toward an older, blue truck on the night she was killed.

Smith owned a 1967 blue and white GMC truck, according to a court affidavit.

Crabb said he was impressed with how Zouari, now 28, didn't allow the defense to twist her words. Through a victim-witness coordinator, Crabb passed on condolences to Zouari from the entire jury.

On Tuesday, the jury learned about Smith's criminal past. He has convictions for burglary in 1983, first-degree sexual assault in 1989 and aggravated motor vehicle theft in 2006.

After deliberating for about 25 minutes, the jury ruled Smith was a habitual criminal.

For the trial, Smith appeared in court in dress clothes. But during Tuesday's hearing, he wore a light blue jail shirt and orange jail pants. Judge Keith Kautz asked Smith about his clothing and the effect it might have on the proceedings.

"Let's just get it over with," replied Smith, who hung his head and stared toward the back of the courtroom for much of the hearing.

Reach Joshua Wolfson at (307) 266-0582 or at josh.wolfson@casperstartribune.net. Reach Cory Matteson at (307) 266-0589 or at cory.matteson@casperstartribune.net.