KAUFMAN COUNTY, Texas (CNN) -- A set of large tire tracks. It's one of the tenuous clues that could help authorities figure out who killed Kaufman County's top prosecutor and his wife. The skid marks near Mike and Cynthia McLelland's home appear to be from two large vehicles.

But other than that, the case is still a giant mystery.

Authorities don't know who killed the McLellands over the weekend or who gunned down the district attorney's chief felony prosecutor, Mark Hasse, in January.

But officials and residents across Texas are trying to make sure such attacks don't happen again.

A new kind of fear

The impact of the killings has devastated Kaufman County and stunned even followers of local crime.

"We've never had to live with this kind of fear," said Tassie Gamble, president of Kaufman County Crime Stoppers. "We have burglaries, and we have thefts. We don't have murders."

If the assailants don't talk, Gamble hopes money will.

The local Crime Stoppers is coordinating rewards for information leading to the arrest and indictment of those who killed Hasse and McLelland.

Typically, the program offers no more than $1,000 for each crime solved. But it funneled virtually all its reserves and donations -- about $100,000 -- into a reward for the Hasse case.

Gamble said the Hasse reward has "totally depleted" its general fund, but the group won't stop appealing for reward donations and tips in the McLelland case.

"There's always somebody out there who knows something," she said.

Theories abound

With little solid information, speculation on who is behind the killings has included a white supremacist gang targeted by Texas and federal authorities last year, drug cartels and someone with a personal grudge against the slain prosecutors.

The white supremacist angle gained traction in part because McLelland, in an interview with The Associated Press before his death, speculated that the Aryan Brotherhood of Texas could have been behind Hasse's slaying.

"We put some real dents in the Aryan Brotherhood around here in the past year," McLelland told the news agency.

McLelland said he wasn't involved in the Aryan Brotherhood investigation, but his office was one of numerous Texas and federal agencies involved in a multiyear investigation that led to the indictment last year of 34 alleged members of the group -- including four of its senior leaders -- on racketeering charges.

While authorities have not said whether they have linked the deaths of Hasse and McLelland or the involvement of white supremacists, Texas law enforcement agencies did warn shortly after the November 2012 indictment that there was "credible information" the group was planning to retaliate.

He thinks drug cartels concerned about disruptions in the methamphetamine supply are more likely culprits.

Peter Schulte, a friend of the McLellands and a criminal defense attorney who worked in the county, speculated that the killings were "personal."

"If this was a case that somebody was trying to change, they would have been going after witnesses and not the prosecuting attorney," Schulte said.

Safety concerns spread

The prosecutor slayings in Kaufman County have led to an unparalleled rise in security.

"I can promise you that all of the people in this courthouse, all of the elected officials, all of the other people who are involved in this investigation are being very well-protected," County Judge Bruce Wood told reporters Tuesday.

Just to the west, Dallas County District Attorney Craig Watkins leads the second-largest district attorney's office in the state. He said officials are taking steps to protect the county's more than 200 prosecutors.

"We have a plan in place that will not only protect me, but every prosecutor," Watkins told CNN affiliate WFAA on Tuesday. He would not provide details of the plan.

Carmen Castro, the public information officer for the Dallas County Sheriff's Department, said security measures will be reviewed and implemented at county buildings.

In light of the Kaufman County homicides, Watkins said he believes his three children and wife are now more concerned than he is.

"All three of our kids slept in bed with us last night," he said.

And in Houston, Harris County's district attorney will be under 24-hour security, the sheriff's department said.

Authorities swarm rural community

Hundreds of investigators -- from local officials to the Texas Rangers to the FBI -- have descended on Kaufman County.

The roughly 100,000 residents can do little but nervously watch and hope.

"The residents are, I think, astounded," said Delois Stolusky, who has lived in Kaufman, the county seat, for 30 years. "It's just, one and one make two. You can't keep from connecting these. And it's just scary because we have no clue of who did the first shooting. And no clue, of course, yet, who did this one. And so, of course, our concern is what's going to happen next."

Law enforcement analysts say they believe those responsible had been monitoring and following the two prosecutors, given the locations of the attacks and the brazenness of killing the men where they were most comfortable.

'A trying time for all of us'

The district attorney's office, which has about a dozen prosecutors, has kept a low profile since the killings. But it released a statement saying it, too, is trying to grapple with the tragedies.

"We would like to thank everyone for their thoughts and prayers for the family and co-workers of Mike and Cynthia McLelland; they, and the support that we have received in the last two days are greatly appreciated," the statement read.

"This is certainly a trying time for all of us both professionally as an office, and personally as friends and co-workers of Mr. McLelland and his wife. Our thoughts and prayers go out to their families."

Kaufman County government offices will close Thursday to allow employees to attend a public memorial service in honor of McLelland and his wife, Wood said. A funeral will follow on Friday.

Brandi Fernandez, McLelland's first assistant district attorney, has been named to lead the office on an interim basis. She will fill that role until the governor appoints a successor.

But whoever becomes Kaufman County's next top prosecutor will have to grapple with the haunting past, Kaufman city Mayor William Fortner said.

"I wonder if the governor is going to find anyone brave enough to take the job of district attorney."

Gary Tuchman, Ed Lavandera reported from Kaufman County; Holly Yan reported and wrote in Atlanta