Officials hold a press conference on scene at the Marjory Stoneman Douglas High School where a gunman killed 17 people in Parkland, FL, United States, on Feb 15, 2018. (Xinhua/Monica McGivern)

WASHINGTON, Feb. 16 (Xinhua) -- The Federal Bureau of Investigation (FBI) admitted Friday that it received a tip in January on Nikolas Cruz, the Florida school shooter who killed 17 people earlier this week, but failed to follow up.

The FBI said in a statement that a person close to the shooter called the agency's tip line on January 5 to warn about "Cruz's gun ownership, desire to kill people, erratic behavior, and disturbing social media posts, as well as the potential of him conducting a school shooting."

The statement came two days after Cruz, 19, opened fire with an AR-15 rifle at students and teachers at Marjory Stoneman Douglas High School in the city of Parkland in Broward County, just north of Miami on the state's southeastern tip.

Besides the 17 killings, the shooting also injured 14 others.

Thousands of the South Florida community gather at Pine Trails Park on Feb.15, 2018 to honor the 17 fallen victims of the recent Florida school shooting. (Xinhua/Monica McGivern)

"Under established protocols, the information provided by the called should have been assessed as a potential threat of life," the FBI statement said. "The information then should have been forward to the FBI Miami Field Office, where appropriate investigative steps would have been taken."

The FBI said that those protocols were not followed for the January tip, therefore the information was not provided to the Miami office, and no further investigation was conducted at that time.

The flag above the White House is lowered to half-staff for the shooting victims of a mass shooting in a South Florida High School, in Washington D.C., United States on Feb 16, 2018. (Xinhua/Ting Shen)

Wednesday's massacre raised concerns about potential failure in school security and sparks ongoing U.S. debates on gun control.

"We are still investigating the facts," FBI Director Christopher Wray said. "We have spoken with victims and families, and deeply regret the additional pain this causes all those affected by this horrific tragedy."

Cruz, who was expelled from the school for disciplinary reasons, made a brief court appearance on Thursday and was ordered held without bond.