A gunman killed 27 people — including 20 kids at Sandy Hook Elementary School in Newtown, Conn, — and then shot himself.

The school shooting is one of the worst in history.

The gunman, identified as Adam Lanza, was reportedly wearing all black, a mask and a bullet-proof vest while carrying Glock and Sig Sauer 9mm handgun. A .223 Bushmaster rifle was found in his car.

The 20-year-old reportedly shot and killed his mother, Nancy Lanza, who was a kindergarten teacher at the school, while firing dozens of rounds in two rooms before shooting himself in the kindergarten classroom.

CNN reported the principal and a school psychologist were killed in the shooting, which was reported at 9:41 a.m. The News York Times' Libor Jany also cited witnesses who are saying the school's principal was killed.

News reports detailed heroic acts by teachers, including one who physically stood in front of the door to keep it shut and protect her students.

First-grade teacher Kaitlin Roig told ABC News she locked her students and herself in the bathroom and was so intent on keeping them alive she initially refused to unlock the door for the police, fearing the gunman was trying to trick her into opening the door.

Following the shooting, Police were "questioning a handcuffed suspect in connection with the Newtown school shooting," the Connecticut Post tweeted. A witness told Jany that a man "was led out of the woods by police in handcuffs." Connecticut State Police Lt. J. Paul Vance told reporters that there was only one shooter.

It was initially reported that Adam's brother, 24-year-old Ryan Lanza, was the shooter and a couple of media outlets broadcast his picture on air before retracting the report.

The confusion may have been caused by the fact that the shooter was carrying his older brother's ID, Reuters' Matthew Keys tweeted around 4 p.m. on Friday. The Associated Press reports that a law enforcement official mistakenly transposed the brothers' first names.

Police are questioning Ryan Lanza, who is reportedly not a suspect.

Ryan Lanza told friends that he thinks his developmentally disabled brother may have committed the crime, according to Patch. A source told The New York Post Ryan told investigators he last saw Adam in 2010 and that Adam is autistic.

Neighbors described the younger man to ABC as “odd” and displaying characteristics associated with obsessive-compulsive disorder.

USA Today reports that the police found another adult male at a Newtown home owned by Nancy and Peter Lanza.

A senior law enforcement official told CNN says that one of the shooter's brothers was found dead in a home searched in Hoboken, New Jersey, but CNN now reports that no body found there.

Here is President Barack Obama's statement after the shooting: