The Florida sheriff whose department responded to this month's high school massacre defended his leadership Sunday while insisting that only one of his deputies was on the scene as the gunman killed 14 students and three staff members. Broward County Sheriff Scott Israel told CNN that investigators are looking into claims that three other deputies were on the scene but failed to enter the school when the chance to save lives still existed. Israel and the sheriff's office have come under withering scrutiny after last week's revelation that deputy Scot Peterson did not go in to confront the suspected shooter, 19-year-old Nikolas Cruz, during the Valentine's Day attack. It is also facing backlash for apparently mishandling some of the 18 tipster calls related to the suspected shooter. The tips were among a series of what authorities now describe as the clearest missed warning signs that Cruz ... posed a serious threat. The FBI has acknowledged that it failed to investigate the tip about Cruz that the agency received on Jan. 5. A transcript of the phone call [to the FBI] spanned more than 13 minutes. During the call, the woman described a teenager prone to anger with the mental capacity of a 12 to 14 year old" that deteriorated after his mother died last year. She pointed the FBI to several Instagram accounts where Cruz had posted photos of sliced-up animals and rifles and ammunition he apparently purchased with money from his mother's life insurance policy. "He's thrown out of all these schools because he would pick up a chair and just throw it at somebody, a teacher or a student, because he didn't like the way they were talking to him."