Suspicion in the murders of a Texas district attorney and his wife has shifted to a violent white supremacist prison gang.
It was the focus of a December law enforcement bulletin warning that its members might try to attack police or prosecutors.
The weekend deaths of Kaufman County District Attorney Mike McLelland and his wife, who were found shot in their home, were especially worrying. They happened just a couple of months after one of the county's assistant district attorneys, Mark Hasse, was killed near his courthouse office.
And less than two weeks ago, Colorado's prison chief was shot to death at his front door, apparently by a white supremacist ex-convict who died in a shoot-out with deputies after fleeing to Texas.
The Aryan Brotherhood of Texas has been in the state's prison system since the 1980s, when it began as a white supremacist gang that protected its members and ran illegal activities, including drug distribution, according to Terry Pelz, a former Texas prison warden and expert on the gang.
The group, which has a long history of violence and retribution, is now believed to have more than 4,000 members in and out of prison who deal in a variety of criminal enterprises, including prostitution, robbery and murder. It has a paramilitary structure with five factions around the state, Mr Pelz said.
Four leaders of the group were charged in October over crimes ranging from murder to drug trafficking. Two months later, authorities issued the bulletin warning that the gang might try to retaliate against law enforcement for the investigation that also led to the arrest of 30 other members.
At the time, prosecutors called the charges "a devastating blow to the leadership" of the gang.
Mr McLelland was part of a multi-agency task force that investigated the Aryan Brotherhood with help from the FBI, the Drug Enforcement Administration and police in Houston and Fort Worth. He and his wife Cynthia were found shot to death on Saturday in their rural home just outside the town of Forney, about 20 miles from Dallas.
Meanwhile, law enforcement agencies throughout Texas were on high alert, and steps were being taken to protect DAs and their staffs. In Kaufman County, deputies escorted some employees into the courthouse after the killings stirred fears that other public workers could be targeted.