In tearful testimony, Seth Fontenot said he is still haunted by the fatal shot he fired that struck 15-year-old Austin Rivault.

Fontenot, who maintains he wanted only to scare burglars trying to break into his truck, took the witness stand Monday in his first-degree murder trial for killing Rivault and wounding two other 15-year-olds in 2013.

Prosecutor J.N. Prather has argued the shooting was intentional and has denied the teenagers were up to no good.

Fontenot testified Monday that he “couldn’t believe it” when a detective interviewing him the morning after the shooting told him he had killed someone.

“How do you feel today?” his defense attorney, Thomas Guilbeau, asked.

“Like a monster,” Fontenot said.

“It’s been two years and one month since that shooting. Does it ever leave your mind?” Guilbeau asked.

“No, sir. It doesn’t,” Fontenot replied, wiping tears from his eyes.

On the witness stand for some four hours Monday, Fontenot recounted in detail the moments leading up the shooting.

He said he was awakened about 1:45 a.m. Feb. 10, 2013, by what sounded like the “popping” of door handles on his locked Chevrolet Avalanche.

Fontenot, who was 18 at the time, said he jumped out of bed, grabbed his 9 wmm Beretta off his desk and then raced to the dining room, where he parted the window blinds and saw two figures in his yard.

“I immediately put my shoes on and ran outside,” he said.

Fontenot, wearing boxer shorts and red Converse sneakers, said he saw a truck’s headlights come on and yelled “freeze” and “stop” as the vehicle moved past his house.

He fired three shots, with only a second or two between each one.

One bullet struck Rivault in the head, killing him.

The two other shots wounded Cole Kelley and William Bellamy, both of whom testified last week that they were dropping Rivault off at his home a few doors down from Fontenot’s house on Green Meadow Road and had no idea why someone in his underwear was firing at them.

“I was frustrated and a little angry,” Fontenot said when Guilbeau asked why he pulled the trigger.

“What were you angry about?” Guilbeau asked.

“Being the victim of multiple burglaries,” Fontenot replied.

Fontenot said he didn’t want to hurt the people in the truck, just scare them, and aimed first at the front driver’s side tire and then the tailgate.

Guilbeau worked to paint a picture of a teenager who had rarely handled a pistol and could never have intentionally hit three people in a moving truck in the dark.

Fontenot said he and his stepfather purchased the gun less than two months earlier at Lafayette Shooters.

There had been one burglary and one attempted burglary of his truck, Fontenot said, and someone had stolen his mom’s purse out of her vehicle in their driveway.

“I felt very unprotected,” he said.

Fontenot said he never owned a pistol before he bought the Beretta and had fired his new gun only once before the February incident.

Fontenot is scheduled to return to the witness stand at 9:30 a.m. Tuesday for questioning by Prather, who had just begun his cross-examination when court recessed Monday.

In opening statements last week, Prather told jurors it was no accident that Fontenot’s bullets hit the three boys.

He was aiming for them, Prather said, taking intentional “head shots.”

“Three shots, three hits,” he said.

Prather already has pointed to text messages from Fontenot a month earlier in which he wrote about buying a pistol and shooting anyone he caught breaking into his truck.

Under questioning from Guilbeau on Monday, Fontenot said he wrote the text messages in anger after someone had egged his truck.

“I was trying to act big and bad with my girlfriend, whoever I was talking to,” he said.

Fontenot faces life in prison if convicted on the murder charge.

Follow Richard Burgess on Twitter, @rbb100.