Kaufman County, Texas (CNN) -- While speculation swirls around them, investigators in this north Texas county are leaving no stone unturned as they dig for clues into who killed two prosecutors.
Theories have included hits by grudge-holding drug cartels or by a white supremacist gang targeted by Texas and federal authorities last year.
CNN has learned that beyond those possible scenarios, tight-lipped investigators are looking at local public corruption cases in Kaufman County.
One example involves an official convicted last year.
Since the January 31 daytime slaying of chief felony prosecutor Mark Hasse outside the courthouse, authorities have pored through his case files.
Saturday night, hours after Hasse's boss, District Attorney Mike McLelland and his wife, Cynthia, were found dead at their home, investigators met at a local Denny's restaurant with the convicted official, his attorney told CNN on Tuesday.
Investigators took swab samples from Eric Williams' hand to test him for gun residue, attorney David Sergi said. CNN does not know what the results of those swab tests have revealed to investigators.
Sergi says his client voluntarily cooperated because he has nothing to hide.
Williams, a former justice of the peace, was convicted of burglary and theft by a public servant and was sentenced to two years' probation.
He told North Texas TV station KXAS he understands why authorities would want to meet with him after the McLellands' death.
"If I was in their shoes, I would want to talk to me," Williams said. "In the investigators' minds, they want to check with me to do their process of elimination."
Williams said he has cooperated with law enforcement.
"I certainly wish them the best in bringing justice to this incredibly egregious act," he said.
Williams told the station he has no ill will toward prosecutors, saying they were "doing their jobs."
The probe into local cases shows investigators are looking at much more than possible cartel or Aryan Brotherhood of Texas connections to the cases.
They are looking through all the McLelland and Hasse case files to see if any red flags arise.
County Judge Bruce Wood said "literally hundreds" of investigators are working the case.
"I'm not sure what time frame we're on, but I'm confident that they will find whoever committed this crime," he told reporters Tuesday.
The investigation is starting from scratch, with no leads in the McLellands' deaths, CNN affiliate WFAA reported.