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Already facing criticism for how it handled the warning signs about shooter Nikolas Cruz, the Broward County Sheriff’s Office could now see a state investigation over its response to the deadly February 14 school shooting.

On Sunday, Florida Gov. Rick Scott asked the Florida Department of Law Enforcement to “immediately investigate the law enforcement response” to the shooting at Marjory Stoneman Douglas High School, according to a news release from his office.

Broward County Sheriff Scott Israel said in a statement that his department “will fully cooperate” with the probe, “as we believe in full transparency and accountability.”

Israel has been under growing pressure as Florida Speaker of the House Richard Corcoran, along with 73 other Republican state representatives called on the governor to suspend Israel for “incompetence and neglect of duty” in a letter sent Sunday.

They said that he and his deputies failed to “intervene regarding Nikolas Jacob Cruz in the years, months, and days leading up to that shooting,” which Corcoran described as “unacceptable and unforgivable.”

“Sheriff Israel failed to maintain a culture of alertness, vigilance, and thoroughness amongst his deputies. … As a result of Sheriff Israel’s failures. students and teachers died.” the letter said.

Amid calls for his suspension, Israel, a Democrat, told CNN’s Jake Tapper on Sunday that he will not step down.

More questions have been raised as details of law enforcement’s response before and during the shooting have emerged.

Law enforcement including the FBI and local authorities received warnings about Cruz before the attack, including one caller saying the eventual gunman could be a “school shooter in the making.”

The sheriff’s office said it received several calls related to Cruz in the past decade. Israel said investigators are looking into the handling of at least two calls that may tipped law enforcement to Cruz.

Read the transcript of the interview with Sheriff Israel

When questioned about red flags brought to law enforcement’s attention, Israel said: “I can only take responsibility for what I knew about. I exercised my due diligence. I’ve given amazing leadership to this agency.”

What happened during the shooting?

There have also been questions about how Broward County deputies responded during the critical moments of the shooting in Parkland, Florida.

During the shooting, the armed school resource officer assigned to the school stayed outside the building where the shooting was taking place, authorities said. Scot Peterson took cover outside the school as bullets flew for four minutes and “never went in,” Israel had said.

“I was disgusted. I was just demoralized with the performance of former deputy (Scot) Peterson,” Israel said Sunday.

Peterson had received active shooter training, according to a letter Israel had written in response to Florida state representative Bill Hager who wrote a letter urging the governor to remove Israel from his post for his deputies’ “unfathomable inaction” during the massacre.

Peterson resigned last week following his suspension.

Questions have also mounted over what happened during the shooting. CNN reported earlier that sources said Coral Springs police officers arrived at the site of the shooting and were surprised to find three other Broward County Sheriff’s deputies, in addition to Peterson, had not entered the school.

Israel said his department is also looking into the reports that the deputies didn’t enter the school building during the shooting. But he said, as of now, Peterson was the only officer that he was certain had been derelict.

“We will get to the truth. But, at this point, one deputy was remiss, dereliction of duty, and he’s now no longer with this agency. And that’s Peterson,” Israel said Sunday.

He added that his department’s investigation so far indicates the Coral Springs officers didn’t arrive until about four minutes after Cruz had left the campus.

A report on what Coral Springs officers observed is expected. Sources caution that surveillance video is currently being reviewed and official accounts could ultimately differ from recollections of officers on the scene.

Return to campus

As the investigations continue, students of Stoneman Douglas returned to campus Sunday for a voluntary campus orientation.

Armed deputies were on campus and will also be on hand when students return to class Wednesday

Grappling with trauma, students and their parents made an emotional return to campus for the first time since the shooting. Some wore school T-shirts that read: “MSDStrong.”

“It was really scary. I didn’t know how I was going to feel when I went in and I saw the fence around the freshman building … and all the windows were covered,” sophomore Tanzil Phillip told CNN.

The building where the shooting occurred will remain closed.

He said students met in the theater room, “and we just gave each other hugs.”

Related: These are the victims of the Stoneman Douglas shooting

School officials are working with students who don’t want to return to Stoneman Douglas and arranging for them to transfer.

Broward County Public Schools Superintendent Robert Runcie said officials will be accommodating and take measures like adding counselors and service dogs in classrooms.