FBI officials declined to say what precise searches were used to try to identify the owner of the account or to possibly link it with other social media profiles. Cruz had two Instagram accounts that also contain his name: cruz_nikolas and nikolascruzmakarov.

A law enforcement official said the FBI will review the steps it took in responding to the tip to determine whether anything could have been done differently or if practices should be changed for the future.

A search of the public records database Nexis for people with the name “Nikolas Cruz” returns 22 results, three of which use different spellings. It was not immediately clear if the FBI attempted to contact any of those people.

Without more to go on, officials felt there wasn’t enough legal justification to issue a subpoena to YouTube for the underlying information about the “nikolas cruz” who had threatened a school shooting, a law enforcement official said.