FORT LAUDERDALE, FLORIDA (NYTIMES) - The only armed security guard on campus during a deadly mass shooting at a Florida high school last week "never went in" to a building to try to take down the shooting suspect, Sheriff Scott Israel of Broward County said at a news conference Thursday (Feb 22).

Scot Peterson, a sheriff's deputy, resigned Thursday after Israel placed him under an internal affairs investigation for failing to meet the standards of the sheriff's office.

Two other deputies, Edward Eason and Guntis Treijs, have been placed on restricted duty while the department investigates whether they could or should have done more to stop the shooter.

Police protocol requires confronting shooting suspects as quickly as possible. Peterson should have "went in, addressed the killer, killed the killer," Israel said at a news conference in Fort Lauderdale.

Instead, the deputy remained outside the freshman building at Marjory Stoneman Douglas High School in Parkland, on Feb 14 for "upwards of four minutes" while the shooting suspect, Nikolas Cruz, was inside.

Cruz is accused of killing 17 people in less than six minutes.

Surveillance video showed Peterson was doing "nothing," Israel said.

Israel described himself as "devastated, sick to my stomach." "There are no words," he said.

Israel, flanked by two of his top aides, appeared emotional during the news conference where he described Peterson's conduct. His eyes appeared to glisten, and his speech was sometimes halting.

The New York Times reported on Wednesday that an officer from the Coral Springs police department who responded to the shooting had seen Peterson in a Stoneman Douglas High parking lot.

The deputy "was seeking cover behind a concrete column leading to a stairwell," Officer Tim Burton said.