The withdrawal of an assistant US attorney from a major racketeering case in Texas appears tied to personal concerns about a white supremacist prison gang's propensity for violence.

The case involves charges against 34 members of the Aryan Brotherhood of Texas, a group investigators say may be tied to the shooting death of Kaufman County District Attorney Mike McLelland and his wife in their home Saturday, as well as to the death two months earlier of county prosecutor Mark Hasse, who was shot and killed in a parking lot near the county courthouse.

Mark Potok of the Southern Poverty Law Center, which tracks hate groups, describes the Aryan Brotherhood of Texas (ABT) as “arguably the most violent white supremacist prison gang out there.”

"It is said to be one of the gangs that live by the 'blood-in, blood-out' code, meaning that you can only get into ABT by carrying out some kind of attack," Mr. Potok told CNN. "And similarly ... you can only leave in a body bag."

The all-white gang formed some time in 1980s, first as a form of self-protection inside prisons, then as a criminal enterprise beyond prison walls with a military structure. It’s believed to have about 4,000 members, including many who have finished their sentences and are out of prison.

“Unlike [Branch Davidian leader] David Koresh and his sheeplike followers (and other sects based on religious fanaticism), these are battle-hardened and death-tested men (many of them … with extensive military experience) who are not set on dying for some kind of religious cause; their thing is that, when the situation calls for it, they’re killers,” writes a former prison inmate on the Daily Beast website. “They’re not into dying – except to protect the honor of the Brotherhood.”

“They’re also sincere in their belief that many members of law enforcement are kindred spirits, right-wingers who understand their hatreds, loss of hegemony, and rabid determination to protect whatever power the white man has left in America,” writes the former inmate – anonymously because of the potential for violent retribution. “And those who don’t buy into their hateful rhetoric they perceive as being weak-kneed sob sisters who will willingly mongrelize and sell out their proud white heritage. Truly, everyone who is not with them is against them.”

In an e-mail Tuesday, Assistant US Attorney Jay Hileman notified lawyers involved in the statewide racketeering case that he was off the case, Richard O. Ely II, a Houston-based defense attorney who is representing one of the 34 defendants, told the Dallas Morning News.

“It’s shocking because he’s not the kind of guy that I would think that would back away from a challenge,” said Brent Mayr, another defense attorney in the racketeering case. “It would lead me to believe that there are some valid concerns.”

In December, the Texas Department of Public Safety warned that the Aryan Brotherhood could be conducting surveillance against law enforcement officers as part of planned retaliation against those who helped secure the indictments, the Dallas newspaper reports. Since the investigation into the Aryan Brotherhood began in 2008, more than 60 defendants from across the state have been charged and more indictments are expected.

Charges include murder as well as drug dealing. Several defendants have already agreed to testify against fellow gang members.

The pattern in Texas appears to be the same as in Colorado, where evidence points to former state prison inmate Evan Ebel – a member of another white supremacist prison gang, 211 Crew, also known as the Brotherhood of the Aryan Alliance – as the shooter in the recent death of Colorado prisons chief Tom Clements as well as of a pizza delivery man. A few days later, Mr. Ebel was killed in a shootout with police in Texas.

Mr. Clements had begun cracking down on such gangs since taking over the Colorado prison system two years ago. In Ebel's case it appears he was paroled four years early due to a clerical error and removed the ankle bracelet meant to track his movements – a step that authorities failed to act upon in time.

Over the last century, 14 prosecutors have been killed, according to news reports and statistics kept by the National District Attorneys Association, reports the Associated Press. At least eight of them were targeted in the line of duty.

On Wednesday, a sheriff known for cracking down on the drug trade in southern West Virginia's coalfields was fatally shot. A suspect also was shot and was in custody.

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The anonymous former inmate writing in the Daily Beast traces the current spate of violence tied to prison gangs back to the bombing of the federal building in Oklahoma City on April 19, 1995.

“If these recent killings represent the Brotherhood’s twisted form of retribution, the fact that it has taken so long to begin is all the more chilling,” he writes. “To me this would demonstrate a hard-nosed determination that all citizens should find frightening. We shouldn’t be whistling past the graveyard on these killings.”