CHICAGO — The Chicago Police Department, along with Cook County State’s Attorney Kim Foxx, have announced murder charges in connection to a triple homicide last month on the city’s South Side.

A 16-year-old boy is being charged as an adult and faces three felony counts of first-degree murder and one felony count of attempted first-degree murder in the fatal shootings. The teen was arrested Tuesday at a relative’s home in Hazel Crest.

The shooting happened on Feb. 25 inside a resident on the 8000 block of South Vincennes Avenue.

During a press conference Thursday, Chicago police said investigators had learned the offender was welcomed inside the house as an acquaintance of someone who lived at the residence.

Police said an altercation ensued and the 16-year-old took out a gun and shot all of the victims inside the room. The offender then fled the scene.

A 14-year-old boy, identified as Amere Deese, suffered a gunshot wound to his back and was pronounced dead on the scene.

A 36-year-old man, who suffered a gunshot wound to the chest, and a 20-year-old man, who suffered a gunshot wound to his abdomen, were both taken to the hospital where they were later pronounced dead.

A fourth victim, a 16-year-old boy, was shot in the leg and taken to the hospital in serious condition.

Deese’s grandma, Cynthia Jones, said her grandson told her he was playing video games at a friend’s house.

Several other people inside the residence at the time of the shooting were not injured.

Prosecutors said Antonio Velsco opened fire on multiple people all because he wanted to take a rifle from inside the home.

“Obviously this child is angry about something,” Jones said.

Velasco is facing felony murder and attempted murder charges.

“He has to be held accountable,” Chicago Police Department Superintendent Larry Snelling said. “No excuse for anyone to reach this level of violence.”

Cook County State’s Attorney Kim Foxx said the teen will be tried as an adult.

“Four lives have been changed,” Foxx said. “The victims that have been taken from their families and now this young person, who now faces the grave consequences and accountability for his actions.”

The teen was in court for a detention hearing on Thursday.

He will be back in court on April 9.

Chicago police said they are still looking for a second person of interest in connection with the case.