The brother of the man charged over last month’s Florida High School shooting has been arrested for repeatedly trespassing at the scene of the massacre.

Zachary Cruz, 18, was ordered to be held on bail of US$500,000 ($650,000) for visiting the Marjory Stoneman Douglas High School in Parkland, Florida three times despite requests to stay away.

Cruz reportedly told deputies he went to the campus to “reflect on the school shooting and to soak it in”, according to the arrest report.

But during Cruz’s court appearance on Tuesday, a Broward County prosecutor said school officials had told him to stay away from the campus, where his brother Nikolas Cruz allegedly killed 17 people on February 14.

“Weeks after his brother murdered, injured and terrorised the school, he is there with no legitimate purpose,” Assistant State Attorney Sarahnell Murphy said of Zachary Cruz.

Ms Murphy said Cruz currently lived with a guardian in a nearby county, but gave a false address to police.

A Florida judge last week entered a not-guilty plea for Nikolas Cruz, who faces a possible death penalty.

Nikolas Cruz, 19, chose to remain silent during the March 15 hearing at Broward County circuit court, where Judge Elizabeth Scherer pleaded on his behalf for 17 counts of first-degree murder and 17 counts of attempted murder.

Accused shooter Nikolas Cruz faces the death penalty. Photo: Twitter/Jennifer Tintner

Both brothers lived with a Florida neighbour, Roxanne Deschamps, after their mother’s death in November.

At a news conference in New York City on Tuesday, Ms Deschamps told of her attempts to warn police that Nikolas Cruz had a history of violence and had purchased a gun. 

She said she called 911 three times to tell police he had punched holes in her wall and may have been planning to bury a gun in the backyard.

“I was very concerned that the gun which he had purchased might be brought into my house or that he might get the gun and use is to harm himself and others,” Ms Deschamps read from a prepared statement.

“Law enforcement said nothing could be done,” she said, wiping away tears.

She said she begged Nikolas to see a doctor because “he was very depressed” after his mother’s death, but he refused to take medication.

In the Florida courtroom, Ms Murphy said Zachary Cruz had visited his brother in jail, “where he has been heard and observed discussing how popular his brother is now”.

A defence lawyer for Zachary Cruz said he was not dangerous.

“He is being held because of who he is related to, not because of what he did,” attorney Joseph Kimok said.

Judge Kim Theresa Mollica ordered Cruz to be fitted with an ankle monitor should he post bail and told him to stay at least a mile away from the high school in Parkland.

She instructed him not to have any contact with his brother or anyone at the school.

–with AAP