Florida shooting: FBI admits it failed to investigate warning over massacre suspect Nikolas Cruz

The FBI has admitted it failed to investigate a warning that the teenage Florida school shooting suspect may have been plotting to carry out an attack.

A person close to the weapons-obsessed 19-year-old Nikolas Cruz last month told the law enforcement agency to warn of "the potential of him conducting a school shooting".

But protocols were not followed and the tipline failed to pass on the complaint, the FBI said on Friday.

Cruz has confessed to carrying out the attack at Marjory Stoneman Douglas High School in Parkland, police said, and he has been charged with 17 counts of murder.

On January 5 a person close to the teenager contacted the FBI tipline to provide "information about Cruz's gun ownership, desire to kill people, erratic behaviour, and disturbing social media posts, as well as the potential of him conducting a school shooting", the FBI said in a press release.

FBI Director Christopher Wray said the bureau is "still investigating the facts".

He said: "I am committed to getting to the bottom of what happened in this particular matter, as well as reviewing our processes for responding to information that we receive from the public.”

Florida governor Rick Scott has called on FBI chief Wray to resign after it emerged the agency did not follow up the tip-off.

US senator Marco Rubio also criticised the agency, saying it was "inexcusable" the bureau did not follow protocols.

He said that Congress should launch its own investigations into what happened.

Speaking to reporters after the teenager’s first court hearing, defence attorney Melisa McNeill described suspected gunman Cruz as "sad", "mournful" and "remorseful".

"He is fully aware of what is going on, and he's just a broken human being,” she said.

His defence team added that he shows signs of autism and seems to be suffering from mental illness.