U.S. President Donald Trump in his tweets on Thursday called the suspected gunman in the massacre of 17 people at a high school in southern Florida “mentally disturbed”.

The 19-year-old, identified as Nikolas Cruz, was due in court on Thursday. He is an orphan living with a friend and going through depression.

He was arrested after Wednesday’s shooting spree in Parkland, Florida, at Marjory Stoneman Douglas High School, where the former student had previously been expelled for what school officials said were “disciplinary reasons.”

“So many signs that the Florida shooter was mentally disturbed, even expelled from school for bad and erratic behaviour,” Trump tweeted.

“Neighbours and classmates knew he was a big problem. Must always report such instances to authorities, again and again!”

Authorities said 15 people were hospitalized with injuries suffered in the attack, which occurred late in the school day.

He had been getting treatment at a mental health clinic, but he had stopped. He had been expelled from school for disciplinary problems. Many of his acquaintances had cut ties in part because of his unnerving Instagram posts and reports that he liked shooting animals. His father died a few years ago, and his mother, among the only people with whom he was close, died around Thanksgiving. He was living at a friend’s house. He was showing signs of depression.

And Nikolas Cruz, 19, had a fascination with guns. He owned an AR-15 assault-style rifle.

Although school officials, students and others who knew him were aware that something was off with Cruz, it is unclear whether anyone had a full picture of what was building within him in recent months. Had everyone who knew of his struggles sat down in a room and compared notes about his recent past, perhaps an alarm would have sounded ahead of what emerged on Valentine’s Day, when Cruz allegedly walked into a suburban South Florida high school and carried out one of the nation’s deadliest school shootings.

“Weird” was the word students had used to describe Cruz since middle school. At first “it was nothing alarming,” said Dakota Mutchler, 17, who attended middle school with Cruz, adding that there was something “a little off about him.” But that was it — for a while.

As Cruz transitioned into high school, he “started progressively getting a little more weird,” Mutchler told The Washington Post. Cruz, he said, was selling knives out of a lunchbox, posting on Instagram about guns and killing animals, and eventually “going after one of my friends, threatening her.”