FORT LAUDERDALE (Florida) • Employees will return to work on Friday at the Florida school where a teen gunman shot and killed 17 people in the deadliest shooting ever at a US high school, district officials said, with students expected back next week.

The announcement came as Nikolas Cruz, the 19-year-old former student accused of the shooting, made an appearance on Monday in court for a procedural hearing, his first public appearance since he was held without bond on 17 counts of premeditated murder.

Cruz is accused of entering Marjory Stoneman Douglas High School in Parkland, near Fort Lauderdale, from which he had been expelled last year for "disciplinary reasons", and opening fire with an AR-15 semiautomatic rifle last Wednesday.

The school will hold a voluntary orientation for students and parents on Sunday and hopes to have students resume classes the following Tuesday on a modified schedule, Broward County Public Schools said in a statement late on Monday.

The incident has galvanised advocates for stricter gun control.

Student survivors, teachers and gun safety advocates plan a visit to the state capital of Tallahassee today. They will demand that state lawmakers enact a ban on the sale of assault weapons in Florida.

Meanwhile, at his court appearance in Fort Lauderdale on Monday, the teenager, dressed in orange prison garb, sat with his head bowed before Broward Circuit Court Judge Elizabeth Scherer.

Judge Scherer ruled that a defence motion filed last week remain sealed from public view. The content of the motion was not described in the hearing.

In a second hearing, Broward Circuit Court Judge Charles Greene ordered the release of parts of a 2016 mental health assessment of Cruz by the Florida Department of Children and Families.

The agency had been alerted to posts on Snapchat of Cruz cutting his arms and expressing interest in buying a gun.

The agency's report noted that Cruz suffered from depression and had autism as well as attention-deficit hyperactivity disorder.

But after visiting and questioning the teenager at his home, the department determined that he was at low risk of harming himself or others and closed the case in November 2016.

After his mother died last November, Cruz lived with the family of a high school friend for months. They told interviewers they had no inkling of his violent tendencies, although they knew he had guns.

A succession of agencies, including the Federal Bureau of Investigation, also failed to act upon numerous red flags.

Mr Howard Finkelstein, the Broward County public defender whose office is representing Cruz, has said it was apparent that the teenager had not been given enough help.

"This kid exhibited every single known red flag, from killing animals to having a cache of weapons to disruptive behaviour to saying he wanted to be a school shooter," Mr Finkelstein said.

"If this isn't a person who should have gotten someone's attention, I don't know who is. This was a multisystem failure."

REUTERS, NYTIMES