Kaufman County District Attorney Mike McLelland and his wife Cynthia were found shot dead inside their Forney home on Saturday night, a chilling crime that put law enforcement agencies across Texas on high alert and shook prosecutors, defense attorneys and others in legal circles around North Texas.

Late Saturday night, sources said a .223-caliber assault rifle, similar to an AR-15, was used in the murders, with approximately 14 rounds being fired....

The front door of the McLellands' 3,000 square foot residence was found kicked in, sources added. Kaufman County deputies, the FBI, Texas Rangers, the Texas Department of Public Safety and Forney police are all involved in the investigation.

"It is very unusual to see public officials killed in this manner," said ABC News senior justice correspondent Pierre Thomas on "Good Morning America." "If prosecutors are being executed, this is a nightmare scenario; so that's why you see the ATF and FBI actively assisting."

Late Saturday night, news media was asked to leave their positions near the house as law enforcement agencies widened the crime scene.

A neighbor told News 8 police were outside the house when she returned home around 9 p.m. Saturday. The neighbor said McLelland and his wife were friendly people.

"I'm very very scared," said Vanessa Hernandez. "It's really hard to imagine something like this happening in the neighborhood."

One district attorney in a neighboring county has already asked for increased security, and the McLelland case could lead to additional measures being taken at courthouses throughout the region.

"This appears to be a bonafide mystery... and a potentially chilling one at that," Thomas said.

According to the district attorney's official biography, the McLellands have five children, one of whom is a Dallas police officer.