Five people were killed Saturday morning in two linked shootings in Ascension and Livingston parishes, and authorities are on the hunt for a 21-year-old man believed to be the shooter.

UPDATE: Sunday, Jan. 27 at 8:05 a.m.Theriot has been found in Richmond, Virginia, and arrested.

Dakota Theriot, 21, is suspected of shooting and killing Summer Ernest, 20, whom authorities described as his girlfriend, as well as her father, Billy Ernest, 43, and her brother Tanner Ernest, 17, at their mobile home in Livingston Parish just outside Walker. Theriot is then accused of killing his parents, Elizabeth Theriot, 50, and Keith Theriot, 50, in Gonzales, according to authorities from Livingston and Ascension parishes.

The Livingston Parish Sheriff's Office said in a news release that Dakota Theriot should be considered armed and dangerous. He is reported to be driving a 2004 Dodge pickup truck that's gray on top and silver on the bottom, Louisiana license plate No. C583809, which they confirmed was stolen from the Ernest family. Ascension Sheriff spokeswoman Allison Hudson said Saturday afternoon they believed Dakota Theriot was headed toward Mississippi, as they had tracked the vehicle to the state line. 

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The Ernests' neighbor, Charlene Bordelon, said the two youngest children in the Ernest family ran to her home early Saturday asking for help after the shooting. Bordelon said the two children, both under 8 years old, were home at the time of the shooting but were not injured. Bordelon called 911 after the children told her that their father, brother and sister were dead. 

"She was terrified," Bordelon said of the little girl, tears welling in her eyes. "It's so heartbreaking."

Bordelon and her husband said moments before the children knocked on their door, they heard a truck speed from the home. They said Billy Ernest's wife and the children's mother was at work when the shooting happened at the house. 

The Bordelons described the Ernest family as good neighbors, but said they did not know the older daughter's boyfriend — Dakota Theriot — who had moved in with them recently. But they said they hadn't noticed any issues or fighting.  

"They were nice, very friendly people, just normal, everyday average people,” Charlene Bordelon said.

Donald Bordelon, Charlene Bordelon's husband, said he knew the father, Billy Ernest, well.

"He was a good guy," Donald Bordelon said. "It's terrible."

After that shooting, authorities believe Dakota Theriot drove to his parents' home in Gonzales and shot them both. 

Ascension Parish Sheriff Bobby Webre said Keith Theriot was able to identify his son as the shooter before he died Saturday. Keith Theriot was alive but gravely injured when deputies first arrived at the Gonzales-area home.

"He lived there with the mom and dad for a little while but was recently asked to leave with some disagreements," Webre said. "But no idea why he would do anything like this."

The shooting in Livingston happened just before 9 a.m. Saturday in the 14600 block of Courtney Road on a lot with four mobile homes, all rentals, neighbors said.

Not long after, about 25 miles south, the Theriot couple was shot in the 42000 block of Churchpoint Road, where gravel driveways lead to a mix of mobile homes and single-family houses. The Theriots' home was a gray mobile home. 

"We do not believe the suspect to be in Livingston Parish at this time," Livingston Parish Sheriff Jason Ard said Saturday afternoon. "We are working in conjunction with the Ascension Parish Sheriff’s Office as we believe our case is connected to a homicide investigation in that parish. Our investigation is ongoing."

Officials with both the Livingston and Ascension sheriffs' offices said late Saturday there were "no red flags" from Dakota Theriot's past and he was not on their radar for suspicious or dangerous behavior. Ard said Theriot had been arrested once in Livingston Parish, for drug paraphernalia. He had never been arrested in Ascension.

Dakota Theriot was arrested in April 2017 in St. Charles Parish for marijuana possession and fleeing authorities. Officials reported that Theriot sped away from deputies during a traffic stop where he was asked to step out of his vehicle. The Advocate could not immediately find any other criminal history on Theriot or record of violence.  

Michael Logan, who lives next door to the mobile home where the Theriots were shot, said he didn't know the residents of the mobile home well but had talked to them occasionally when they saw one another outside. He said he had heard arguing coming from the residence lately.

"There's been a lot of yelling matches," usually at night, he said.

Logan said he heard the ambulance arrive early Saturday and was shocked, and unnerved, to later learn what happened. He said deputies also checked a barn behind his house, apparently to see if the shooter was hiding there.

"Any time you hear of a shooting this close to home, it's never good. It never gives you a good feeling," he said.

Authorities encouraged anyone with information to call the Livingston Parish Sheriff's Office at (225) 686-2241, ext. 1, or Crime Stoppers at (225) 344-7867.

Dakota Theriot is wanted on multiple counts of first-degree murder, illegal use of weapons and home invasion, authorities said. 

Follow Grace Toohey on Twitter, @grace_2e.