A US preschool assistant has been accused of fatally shooting her longtime boyfriend, who was also her high school sweetheart, according to police.

Mary Katherine Higdon, 24, faces murder charges after she allegedly pulled the trigger on 23-year-old Steven Freeman at their Georgia home, local news station WSBTV reported.

Higdon claimed the shooting was an accident, but police said the evidence suggested there was intent to kill, reports the New York Post.

Police were called to the couple’s home last Wednesday evening after a report of gunfire at the residence. Freeman was rushed to a local hospital where he died from his injuries.

Neighbours said a hysterical Higdon was outside the home while police were at the scene.

“She was out on the porch with the police officers and she said, she was crying, ‘I didn’t mean to do it. I didn’t mean to do it,’” neighbour Jeanette Head told the news station.

According to WSBTV, police reported allegedly smelling alcohol on Higdon’s breath and said she was allegedly mumbling.

The TV station also reported that police had been called to the home five times in the past year, including for domestic violence and for issues relating to animals.

There was no clarification on what those issues were.

Higdon was arrested on charges for murder and possession of a firearm during the commission of a crime.

The 24-year-old, who is a teacher’s assistant at a local preschool, told police that the gun accidentally went off when she handed it to Freeman.

The couple had been together for seven years after reportedly meeting at high school and their families were close, even spending Christmas together, according to the victim’s uncle.

Family members told the Atlanta Journal-Constitution that the couple had been together for seven years and were high school sweethearts.

“The word devastation doesn’t begin to cover it,” Josh Thacker, Freeman’s uncle, told the newspaper. “It’s hard to get through a couple of minutes without crying.

“We’ve lost two people in this,” he continued. “We’ve lost Steven, but obviously our relationship will be changed with Mary Katherine and my heart goes out to the Higdon family because they are doing the same thing.”

The late man’s obituary read that he “lived a life full of loyalty, love, joy and compassion. He was a friend to everyone, especially if that friend loved fishing and hunting. He had a heart of gold, a bounce in his step, and a sweet Southern drawl.

“Steven showed his love for you through his belly laughs, big smiles, bear hugs, deer meat, always being there for you, and making you feel you were the only other person in the world. He was never afraid to tell you, ‘I love you.’”