Embattled Broward County Sheriff Scott Israel said he had provided "amazing leadership" to his department on Sunday, drawing disbelief from CNN host Jake Tapper.

Tapper pressed Israel during a nearly half-hour interview about the response of his department before and during the Stoneman Douglas high school shooting in Parkland, Florida, that left 17 dead.

Israel announced Thursday that school resource officer Scot Peterson had been suspended and decided to retire rather than be terminated after learning Peterson failed to enter the school during the massacre and engage the shooter.

Israel also defended the conduct of his department in response to the 18 calls its deputies got about the killer, Nikolas Cruz, including fears he could be a "school shooter in the making." No report was initiated upon that tip.

Tapper asked Israel, who participated in CNN's town hall on guns on Wednesday and called for stronger gun control laws, if he could see how the public would be critical when it saw so many red flags go ignored by the department.

"How could there not even be a report on this one?" Tapper asked.

"If that's accurate, Jake, there needed to be a report and that's what we're looking in to, that a report needed to be completed, it needed to be forwarded to our homeland security or violent crimes unit and they would've followed up on it," Israel said.

Tapper noted Israel's conditional remarks, pointing out it was notes from Israel's own department. Israel responded the officer who handled that situation was on restrictive duty.

"I've exercised my due diligence, I've led this county proudly as I always have," he said. "We have restricted that deputy as we look in to it. You know, deputies make mistakes, police officers make mistakes, we all make mistakes, but it's not the responsibility of the general or the president if you have a deserter. You look into this. We're looking into this aggressively, and we'll take care of it and justice will be served."

"Are you really not taking any responsibility for the multiple red flags that were brought to the attention of the Broward Sheriff's Office about this shooter before the incident?" Tapper asked.

"Jake, I can only take responsibility for what I knew about. I exercised my due diligence. I've given amazing leadership to this agency—" Israel started.

"Amazing leadership? Tapper asked incredulously.

"Yes, Jake. There's a lot of things we've done throughout this—this is—you don't measure a person's leadership by a deputy not going into—these deputies received the training they needed—" Israel said.

"Maybe you measure somebody's leadership by whether or not they protect the community," Tapper said. "In this case, you've listed 23 incidents before the shooting involving the shooter and still nothing was done to keep guns out of his hands, to make sure that the school was protected, to make sure you were keeping an eye on him … I don't understand how you can sit there and claim amazing leadership."

Israel said on "16 of those cases," his deputies did everything right and in the five years he had been sheriff, he'd taken the department to a "new level."

"One person didn't do what he should have done," Israel said. "It's horrific. The victims here, the families, I pray for them every night. It makes me sick to my stomach that we had a deputy that didn't go in because I know if I was there, if I was on the wall, I would have been the first in along with so many other people."