KAUFMAN, Texas (CNN) -- Fears that a white supremacist gang or someone else is targeting Texas law enforcement officials spread Monday to Houston, where the chief prosecutor went under 24-hour protection in the wake of the weekend shooting death of his counterpart in a suburban Dallas county.
Kaufman County -- where District Attorney Mike McLelland and his wife, Cynthia, died Saturday -- and Harris County were among numerous Texas and federal jurisdictions that participated in a task force targeting the Aryan Brotherhood of Texas in 2012.
The investigation resulted in an indictment that a federal prosecutor called a "devastating blow" to an organization investigators say is known to use threats and violence against its enemies.
The McLellands were found shot to death in their house.
McLelland's death was the second killing of a Kaufman prosecutor since January 31, when Assistant District Attorney Mark Hasse died in a shooting. At the time, McLelland made a promise to the killer to "pull you out of whatever hole you're in."
While authorities have not said if they have established a link between 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" that members of the Aryan Brotherhood were planning to retaliate" for the indictment.
'On heightened alert'
In Harris County, which includes Houston, Sheriff Adrian Garcia put District Attorney Mike Anderson and his family under 24-hour security in the wake of McLelland's death, said Sara Marie Kinney, a spokeswoman for the prosecutor's office.
Uniformed officers have also been placed outside Anderson's office, she said.
In Kaufman County, the district's attorney's office will remain closed Monday, but the courthouse will reopen under heavy security. Judges and others are also following law enforcement advice on personal security, county Judge Bruce Wood said.
"We are all on heightened alert. There's no question about that," Wood said on CNN's "Starting Point" on Monday, a few hours before the county courthouse was scheduled to reopen.
Investigators at the McLellands' home recovered several shell casings from a .223-caliber rifle, a law enforcement source said Sunday.
Authorities from numerous law enforcement agencies, including the Texas Rangers and the FBI, are investigating the deaths.
While authorities have not offered a motive, speculation quickly fell on white supremacists, whom McLelland had said could be involved in Hasse's death. He died after being gunned down in broad daylight outside the county courthouse. The killing remains unsolved.
Deputy prosecutor's killing
In an interview with The Associated Press after Hasse's death, McLelland said his deputy hadn't been involved in prosecuting white supremacist gangs, but the district attorney nevertheless raised the possibility that Hasse was killed by one.
"We put some real dents in the Aryan Brotherhood around here in the past year," McLelland told the news agency.
In November, a federal grand jury in Houston indicted 34 alleged members of the Aryan Brotherhood of Texas -- including four of its senior leaders -- on racketeering charges. Multiple agencies investigated the case, including officials from the Kaufman County district attorney's office.
At the time, Assistant U.S. Attorney Lanny A. Breuer called the indictment a "devastating blow" to the organization, which he said used threats and violence, including murder, against "those who violate (its) rules or pose a threat to the enterprise."
Hasse had feared for his life and carried a gun to work, said a Dallas attorney who described herself as his longtime friend.
Colleen Dunbar said she spoke with Hasse a week before he died. She said the prosecutor told her he had begun carrying a gun in and out of the county courthouse daily.
"He told me he would use a different exit every day because he was fearful for his life," Dunbar told CNN.
She said that Hasse gave no specifics on why he felt threatened, only that he did.
Before his death, McLelland called Hasse "a stellar prosecutor" who knew that threats were part of the job.
District attorney took precautions
McLelland, a tough-talking Army veteran who later earned a master's degree in psychology and became a psychologist for the Texas Department of Mental Health and Mental Retardation, vowed after Hasse's slaying to put away the "scum" who killed his deputy.
"We're going to pull you out of whatever hole you're in, we're going to bring you back and let the people of Kaufman County prosecute you to the fullest extent of the law," he said.
In the AP interview, McLelland said he began carrying a gun after Hasse's death and was answering his door more carefully.
McLelland's death came 11 days after the similar slaying of Colorado prisons chief Tom Clements -- shot to death March 19 after he answered the door at his home.
While authorities have offered no suggestion the crimes are linked, the man suspected of killing Clements was once a member of a white supremacist group, the 211 Crew. That man, Evan Ebel, died in a shootout with sheriff's deputies in northern Texas.
'Shock waves through the community'
Attorney Pete Schulte, who has worked in Kaufman County, said the killings have left the community in shock.
"The law enforcement community here is very uncomfortable," he said. "It's really sending some shock waves through the community."
U.S. Rep. Ted Poe of Texas told CNN that people in the community are "very concerned for their own safety."
Kaufman Mayor William Fortner told CNN the fear is pervasive.
"I wonder if the governor is going to find anyone brave enough to take the job of district attorney," he said.
-- CNN's Ed Lavandera reported from Kaufman County; Holly Yan reported and wrote from Atlanta. CNN's AnneClaire Stapleton also contributed to this report.
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