A teacher who used to teach at Liberty High School in New Jersey was among the first to report a school shooting at the school.

The school’s principal and principal assistant were among those injured when the shooter opened fire on the building.

Liberty Principal Dr. James L. McDaniel Jr. said the gunman was in his first year of a new school year and had not been to the school in years.

McDaniel said he is a lifelong student who has never been in danger before and that he was able to call his wife at the time and offer support.

“He was scared, so he was in a situation where he didn’t know what to do,” McDaniel said.

He said that he had called his wife to tell her that he knew that the gunman had just killed someone and had told her that she should call the police.

A police source told ABC News that a school employee called to report that a shooter had entered the building through the basement window and that the shooter fired shots at least three times.

The shooter is described as a white male in his late 20s to early 30s, standing between 5 feet 11 inches and 5 feet 9 inches tall and weighing about 250 pounds, according to the source.

He had a handgun, which is not uncommon for school shooters, McDaniel added.

McDaniel, who is from Delaware, said that his son and daughter-in-law were among the students who were shot, but he did not know their names.

When the gunman walked into the school, he was not wearing a mask and had a knife in his hand, McAdams said.

“I think that was an act of desperation,” McAdams told ABC affiliate WNJN.

While school officials were in the building and evacuated, the school lockdown was lifted at about 10:30 a.m. local time, according a school district spokesperson.

The gunman was able, according the school district, to enter the building, which contained classrooms, classrooms, a cafeteria, and the library.

Authorities in the district say they were able to capture the gunman and take him into custody.

There were no reports of injuries from the shooting.

An official with the New Jersey State Police said the shooter was taken to a local hospital.

The suspect is described by authorities as a black man in his 20s, with a thin build, short, curly brown hair, and a mustache, the official said.

He had a history of mental illness and was described by the police as a “violent and unstable individual.”

“We do not believe he has a connection to any other school or community,” McDonough said. 

The Associated Press contributed to this report.