Elected officials outside of Dallas were given extra security Sunday after a local district attorney and his wife were shot to death inside their suburban home, Kaufman County Sheriff David Byrnes said.

The bodies of Kaufman County District Attorney Michael McLelland and his wife Cynthia were found Saturday, just two months after another prosecutor in the county was murdered on his way to work.

No suspects or motives have been identified in any of the three murders.

Byrnes said it wasn't clear the three murders were connected. "We have nothing indicating that for sure," he said.

But elected officials believe the three murders are linked. "It does appear that these are targeted attacks,'' said Darren Rozell, mayor of Forney, where the district attorney lived.

McLellan, 63, and his wife Cynthia, 65, a psychiatric nurse at a state hospital, were probably killed Friday night when neighbors heard shots that they mistook for thunder during a storm. Friends discovered the bodies Saturday, and the sheriff's office was called about 6 p.m.

WFAA-TV in Dallas reported that 14 shells from a .223 caliber rifle were found at the scene. The station also reported that the district attorney's body was found in the hallway and his wife in a front room. USA TODAY could not independently verify the information.

Investigators have not yet connected to killings to the murder of assistant district attorney Mark Hasse, 57, one of a dozen prosecutors who worked for McLelland.

The FBI and Texas Rangers have joined local authorities in the investigations. Hasse was shot just before 9 a.m. on Jan. 31 after he got out of his car in a parking lot behind the county courthouse on his way to work.

"There will be increased security at the courthouse tomorrow -- visible security," the sheriff said.

"This is unnerving, unnerving to elected officials. It's unnerving to the community at large," Byrnes said.

Investigators in Hasse's shooting had various theories, including the possibility that the violent white supremacist gang, the Aryan Brotherhood of Texas, was involved in the killing.

In November, the FBI announced that 34 members of the Aryan Brotherhood, including four senior leaders, were indicted by a federal grand jury in Houston for racketeering.

Robert Kepple, executive director of the Texas District Attorney's Association, said Sunday that law enforcement and his members — about 5,000 prosecutors across the state — received a bulletin late last year from Texas Department of Public Safety, warning that the Aryan Brotherhood might be plotting retaliation against law enforcement officials.

"Our people took notice of that, but it is hard to guard against these kinds of acts,'' said Kepple, who cautioned that investigators had not yet linked the latest killings to gang-related retaliation. "I know that is the working theory, but I don't want to prejudge this.''

The FBI checked to see if Hasse's killing was connected to the Mar. 19 killing of Colorado Department of Corrections chief Tom Clements, who was gunned down after answering the doorbell at his home.

Evan Spencer Ebel, a former Colorado inmate and white supremacist who authorities believe killed Clements and a pizza delivery man two days earlier, was killed in a Mar. 21 shootout with Texas deputies about 100 miles from Kaufman County.

Investigators in that case, however, have not found any links to Hasse's murder. A source who has knowledge of the cases but is not authorized to comment publicly told USA TODAY that investigators compared ballistics evidence in both cases but did not find an immediate match.

Although barely two months separate the Kaufman County slayings, murders of prosecutors are still relatively rare.

Before the Kaufman County cases, the last prosecutor murdered in Texas was Gil Epstein, an assistant district attorney in Fort Bend County near Houston in 1996.

Epstein was shot to death in an armed robbery when authorities said the gunman, Marcus Cotton, noticed Epstein's badge. Cotton was executed in 2004.

McLelland was a former platoon leader and company commander in the U.S. Army infantry. Born in the small town of Wortham, Texas, he'd gone to junior college on a football scholarship and got a history degree from the University of Texas at Austin, according to his biography on the county web site.

He got a degree in psychology and got his law degree while working as a psychologist for the state of Texas. He had five children, including a son who is a Dallas police officer.

McLelland was a "well respected prosecutor who pulled together his staff'' following Hasse's slaying, Kepple said. "He (McLelland) was a strong and good public servant.''