SACRAMENTO, Calif. -- More than 250 binders are filled with some 4,000 leads in the hunt for the person who killed Deputy Jeffrey Mitchell along a dark, rural road more than two years ago.

The Sacramento County deputy was slain Oct. 27, 2006. Just before 3:30 a.m. that day, Mitchell sent a message over his in-car computer to dispatch. It said: No plates. White Chevy van with one. Okay.

What happened next isn't exactly known.

Dispatchers and a patrol deputy tried to contact Mitchell again. When he didn't answer, patrol cars rushed to Meiss Road.

"They immediately observed Deputy Mitchell lying on the ground," Detective Tom McCue said.

He'd been shot in the head at close range, with his own gun. Thirteen minutes had passed between the time he sent his message and when the first deputies found him on the side of the road.

"A large struggle took place on this road, behind and around this vehicle," said McCue, who was in charge of processing the scene.

The coroner's report showed Mitchell died of a gunshot wound to the head. He had abrasions and contusions on his arms, especially on his hands.

Sheriff John McGinness, who'd been in command just three months when Mitchell was killed, said evidence indicates the deputy was in a fight for his life -- "that he had at least one adversary, and it was not a lightweight battle," he said.

"There's significant trauma to his body separate and apart from the sole gunshot wound that ended his life, that indicates strongly that he fought hard," the sheriff said.

Search and rescue teams combed the area for clues. Billboards went up announcing a $225,000 reward. And a department and a family buried one of their own.

The sheriff won't share key details to protect the integrity of the case; however, he gave KCRA 3 rare access to the homicide bureau investigation.

Detective Jason Cvitanov, who's been working the Mitchell case since it began, showed the 250 black binders filled with leads; by comparison, a typical big murder case would fill three such binders.

Cvitanov and his partner worked only the Mitchell case for the first year. They follow up on leads as they come in.

"Obviously, the white van continues to be a theory," he said.

Mitchell had described a white Chevy van. Two men on their way to Lake Tahoe spotted a white Chevy van in the Consumnes River just 11 hours later.

"There's kind of an old saying in law enforcement: Two rights to get away from the cops," Cvitanov said. "And oddly enough, the van's path from the crime scene to its final location if it is involved is two rights and a straight shot."

It's an area frequented by methamphetamine users. Inside the van, two people were dead of carbon monoxide poisoning -- a man in the passenger seat, and a woman in the back.

And the passenger seat was empty, "which suggests the probability of a third occupant in the van," McGinness said.

Investigators now say the circumstances are overwhelming -- two people dead in a van that is the exact make and model used in the murder of a deputy. The van is their best lead.

But until they find a direct link, they can't look past any potential leads -- because the bodies in the van didn't match DNA evidence left at the murder scene.

Investigators recovered some DNA, but not enough to run a cold search for suspects already in criminal databases.

DNA science, though, is advancing quickly.

"I think from the samples we have from that scene today, I think the strong likelihood exists to some day be able to identify the suspect," McGinness said.

The department believes it will solve the case.

"We want the phones to ring. We want people to get us any information they have and give us more of a chance to solve this, and not have to wait for science to catch up," Cvitanov said.