Louisiana law enforcement officials are trying to determine what caused a man described as a “nuisance” by neighbors to gun down a West Baton Rouge Parish sheriff’s deputy and her 20-year-old daughter before turning the gun on himself.

Deputy Donna LeBlanc had just arrived Tuesday afternoon at her home in Glynn in neighboring Pointe Coupee Parish when she spotted 29-year-old Gregory Phillips talking to her daughter, Carli Jo LeBlanc, on their porch, the Baton Rouge Advocate reported. Donna LeBlanc's 9-year-old daughter was in the house, locked inside by her older sister.

Pointe Coupee Parish Sheriff Bud Torres told the newspaper that the family, like many of their other neighbors, had a strained relationship with Phillips.

Torres said it appeared that an argument erupted between LeBlanc and Phillips, who had gone back to his truck. At some point, Phillips produced a .223-caliber assault rifle and, approaching LeBlanc on the carport, began firing at the deputy.

LeBlanc, who was armed with her duty weapon, managed to fire three shots at Phillips before she was killed, the Advocate reported. It was not immediately clear if any of the three shots hit her assailant.

Phillips then turned the rifle on Carli LeBlanc, fatally shooting her. Torres told the paper that the gunman tried to get inside the house where the little girl was, but couldn’t because of the locked door.

After banging on the door and failing to get inside, Phillips apparently shot himself, the Advocate reported.

The 9-year-old called 911 to report the murders.

Torres said investigators do not know what brought Phillips to the LeBlanc home or what the argument was about.

"We don't know what the argument was about. We don't have any eyewitnesses," Torres told the Advocate. "There will be parts of this that are lost because the people that were there are dead."

Neighbor James Didier and his wife, Susan, heard the gunshots, but James Didier told the Advocate that he thought they came from hunters in the area. Susan Didier said she thought Phillips was firing his guns in his backyard – one of the problems that neighbors had with him in the past.

"When I heard the little 9-year-old girl scream, I knew something was wrong," Susan Didier said. "I wish I had gone over there, but we didn't know where the shooter was."

Coworkers on Wednesday were mourning LeBlanc, a 22-year veteran of the sheriff’s office.

"Donna would do anything for you as a cop," said West Baton Rouge Parish Sheriff Mike Cazes. "She had a true love for the thin blue line. She got along great with the community. And she was very involved in both her daughters' lives and just would do anything to help someone."

LeBlanc was married to a Louisiana state trooper, the newspaper reported.

The mourning extended onto social media for LeBlanc and her daughter, who nearly died in a serious car crash in July 2014. She required multiple eye surgeries in the aftermath, and was still working through a traumatic brain injury.