An armed security officer on campus where gunman Nikolas Cruz killed 17 people never went inside the high school or tried to engage the gunman during the attack, a Florida sheriff has said. That same officer has now resigned.

“I think he remained outside for upwards of four minutes,” Broward County Sheriff Scott Israel said during a news conference Thursday afternoon. Scot Peterson never went inside after taking a position on the west side of the building.

Peterson, a sheriff's deputy assigned to the school, "was absolutely on campus through this entire event. He was armed, he was in uniform," Israel said.

Israel said Peterson should’ve gone in and “addressed the killer, killed the killer.” He added that after watching the video, hearing witness accounts and getting a statement from Peterson himself, he suspended the officer without pay and started an internal investigation. However, Peterson then resigned.

"It's devastating," Israel said during the conference. "I'm sick to my stomach. These families lost children, we lost coaches."

After speaking with the internal affairs department, Israel decided to put deputies on restrictive duty while his office investigates “whether or not they could have done more, or should have done more.”

Source: nbcnews.com