The fatal shootings of the district attorney, Mike McLelland, 63, of Kaufman County, and his wife, Cynthia, 65, stunned law enforcement officials and local residents, many of whom were still shaken by the killing of one of Mr. McLelland's prosecutors, Mark E. Hasse, 57, who was killed on Jan. 31 in a parking lot near the courthouse.
The authorities said it was too early to say if the deaths of Mr. McLelland and his wife were connected to Mr. Hasse's shooting. But the timing of the shootings — and the killings of two prosecutors in a county of 106,000 people in the span of eight weeks — appeared to many officials to be more than coincidence.
"I'm really trying to stress for people to remain calm," said Mayor Darren Rozell of Forney. "This appeared to be a targeted attack and not a random attack." Forney is about 15 miles northwest of the city of Kaufman, the county seat.
Officials from several local, state and federal agencies — including the F.B.I., the Texas Rangers and the Kaufman County Sheriff's Department — were working on the case.
The Kaufman County sheriff, David A. Byrnes, told reporters at a news conference on Sunday that his officers had been called to Mr. McLelland's house shortly after 6 p.m. on Saturday and that the bodies of Mr. McLelland and his wife were then discovered inside. He would not say if there were any signs of forced entry.
Sheriff Byrnes said he had increased protection for other local elected officials and would be tightening security at the courthouse, although he would not go into detail.
"It's unnerving to the law enforcement community, to the community at large," he said. "That's why we're striving to assure the community that we are protecting public safety and will continue to do that."
In the shooting of Mr. Hasse, the authorities said one or two gunmen had gotten out of a gray or silver sedan, opened fire and fled. Witnesses told investigators that the suspect or suspects appeared to have had their faces covered and were wearing black clothing and tactical-style vests. No arrests have been made, and investigators from nine agencies have been searching for leads.
After Mr. Hasse's killing, Mr. McLelland appeared alongside the county sheriff and the police chief from the city of Kaufman, vowing to find those responsible and referring to the suspect or suspects as "scum."
"I hope that the people that did this are watching, because we're very confident that we're going to find you, 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 told reporters.
Doug Lowe, the district attorney in nearby Anderson County and a friend of Mr. McLelland's, said the latest shootings "were a blow to all Texas prosecutors."
"We're a tight-knit group," Mr. Lowe said. "I don't think anyone in my group will be in fear. We're not going to let this stand in the way of getting the bad guys."
One of several angles that investigators have been exploring is whether Mr. Hasse's killing involved members of the Aryan Brotherhood, the white supremacist gang that is active in prisons. Prosecutors in Mr. McLelland's office had assisted in investigations of the gang, including a recent case that had targeted the Brotherhood's leadership.
In that case, the federal authorities announced in November that a grand jury in Houston had indicted more than 30 senior Brotherhood leaders and other members of the gang on racketeering charges. Federal officials said the defendants had agreed to commit killings, robberies, arsons and kidnappings and to traffic narcotics on behalf of the gang. The indictments stemmed from an investigation led by a multi-agency task force that included prosecutors from Kaufman County and three other district attorney's offices. A month later, the Texas Department of Public Safety issued a statewide bulletin warning officials that the Aryan Brotherhood was planning to retaliate against officials who had helped secure the indictments.
Mr. Hasse was shot the same day that two Aryan Brotherhood members — Ben Christian Dillon, also known as "Tuff," of Houston, and James Marshall Meldrum, who nickname is "Dirty," of Dallas — pleaded guilty to racketeering charges in Federal District Court in Houston.
A law enforcement official said there was no evidence so far in the investigation of Mr. Hasse's killing that pointed to the Aryan Brotherhood of Texas. The official, who spoke on the condition of anonymity because the investigation was still continuing, said that investigators believed the shootings of Mr. Hasse and Mr. McLelland were related but appeared to have been carried out by different people, perhaps from the same group or with the same affiliation.
But Sheriff Byrnes said he had no indication that the shootings of Mr. McLelland and his wife were the work of the Brotherhood.
Investigators have also been pursuing possible links between Mr. Hasse's killing and the death of Tom Clements, the Colorado state prisons chief, who was shot and killed two weeks ago at his home in Monument, Colo., near Colorado Springs.
The suspect in Mr. Clements's killing, Evan S. Ebel, 28, died after a shootout and high-speed chase with Texas law enforcement officers and sheriff's deputies in Wise County, northwest of Dallas, on March 21. There were a number reports that Mr. Ebel had joined a white-supremacist gang known as the 211 Crew while he was in a Colorado prison, but the authorities said they were still investigating any possible links.
Officials in Colorado Springs who have been investigating Mr. Clements's killing spoke on Sunday with investigators in Texas, but Paula Presley, the undersheriff in El Paso County, Colo., said it was still too early to say whether there were any connections between the killings. She said that Mr. McLelland's killing was "very, very concerning" and that it had raised an already heightened sense of alert in Colorado.
Mr. McLelland was a 23-year veteran of the Army who served in the first Iraq war, according to a biography on the Web site of the Kaufman County district attorney's office. He also worked as a diagnostic psychologist for Texas government agencies.
He served for 18 years as a criminal defense attorney and special prosecutor for the Department of Family and Protective Services. He and his wife had five children, including one son who is a Dallas police officer.
Lauren D'Avolio contributed reporting from Kaufman, and Michael Schwirtz and Serge F. Kovaleski from New York.
This article has been revised to reflect the following correction:
Correction: March 31, 2013
An earlier version of this article, in a quote taken from The Associated Press, misspelled the surname of the Forney mayor as Rovell.
