A teenager and an adult were killed in a school shooting in St. Louis and police won't say how the gunman got into the building

• Three people — including a gunman — were killed in a high school shooting in St. Louis, police said.
• Police have not revealed how the gunman was able to enter the building.

A high school shooting in St. Louis, Missouri left three people dead, including one adult woman, one teen girl, and the shooting suspect, local police said.

It is still unclear how the shooter got into the Central Visual and Performing Arts High School in South St. Louis and police refused to give an answer.

"The doors were locked," St. Louis Police Department Chief of Police Michael Sack told reporters Monday. "The school was closed."

Sack praised the school's security team, saying they did an "outstanding job identifying the suspect's efforts to enter and immediately notified other staff and made sure that we were contacted."

"The door did cause pause for the suspect. It bought us some time," Sack said.

When asked by another reporter how the gunman got into the school if the doors were locked, Sack said "we're not going to talk about that."

Sack noted that the shooting took place on the third floor of the school but it's not clear how the gunman got there.

Sack said that his department got a 911 call about an active shooter at the school at 9:10 a.m. local time.

Within minutes, officers arrived at the scene and went into the school as kids were fleeing out of the building.

The suspect — identified as a man "about 20 years of age" — was carrying a long gun, Sack said.

When police found the shooter in the school, they exchanged gunfire, ultimately hitting the gunman, Sack added.

The shooter was then taken to a local hospital where he was pronounced dead. His cause of death and identity have not been released.

Eight people total, including the gunman, were transported from the school to local hospitals, Sack said.

One of those people was the adult woman who died of gunshot wounds. She was pronounced dead at the hospital as well.

The teen girl who died was pronounced dead at the scene from suspected injuries from gunshots.

Those still being treated in the hospital face a variety of injuries, Sack said, including shrapnel injuries and gunshot wounds. The St. Louis Post-Dispatch reported that someone was being treated for cardiac arrest.

The St. Louis Police Department and Central Visual and Performing Arts High School did not immediately respond to Insider's requests for comment.