The suspect on the run is 21-year-old Dakota Theriot, son of the Livingston Parish victims.
"Deputies sought cover and challenged Theriot, who then dropped the firearm upon their commands and was taken into custody without incident", the sheriff said in a statement to WBRZ.
Authorities say he is considered armed and risky and was driving a 2004 Dodge pickup, gray and silver in color.
Livingston Parish Sheriff Jason Ard confirmed on Facebook that three deaths happened in his parish on Saturday.
"It's been a long time since we've had anything of this magnitude when it comes to domestic violence", Webre said during the press conference. The victims - who were not relatives of the suspect but knew him - have been named as Billy Ernest, 43; Summer Ernest, 20; and Tanner Ernest, 17.
Richmond County Sheriff Stephan B. Smith said in a phone interview that Theriot's grandmother had spent the night in a hotel because she feared her grandson might come to her home in Warsaw.
Crystal DeYoung, Billy Ernest's sister, said they had just started dating. She said she wasn't sure how her niece and Theriot met, but that she believed the relationship was relatively new.
While deputies were there, Smith said, Theriot drove up.
DeYoung said she skipped the birthday party and didn't meet Theriot herself. Summer Ernest is believed to have been in a relationship with Dakota Theriot.
Webre says Theriot traveled to his parents' trailer on Churchpoint Road, went inside and shot both his mother, Elizabeth Theriot, and his father, Keith Theriot, in their bedroom.
Richmond County Sheriff Steven Smith
There were also two young children, ages 7 and 1, in the home at the time of the shooting, he said. The children, both under 8 years old, were not injured in the shooting.
"They all had very good hearts".
"They said something bad happened here". They loved everybody. Never met a stranger.
Charlenne Bordelon lives near the house where the Ernests were killed. They were uninjured and asked for help after the shooting.
In May, he re-posted a message which said: "If you have a problem with me, tell me".
'He lived there with the mum and dad for a little while, but was recently asked to leave with some disagreements, ' Ascension Sheriff Bobby Webre said.
"I would not approach this vehicle".
Theriot is considered armed and risky, Ard said.
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