The armed officer who was assigned to a Florida high school, where 17 students and children were gunned down, took cover outside the building rather than intervening while the shooting unfolded last week.
Deputy Scot Peterson resigned on Thursday after being suspended without pay pending an internal investigation into his actions during the massacre at the Marjory Stoneman Douglas High School campus in Parkland, the New York Times reported.
Peterson never went in after taking a position on the west side of the building, Broward County Sheriff Scott Israel said at a news conference.
The decision to suspend Peterson -- who was armed and in uniform at the time of the shooting -- was made after interviewing the Deputy and reviewing footage and witness statements.
"I am devastated. Sick to my stomach. He never went in," Sheriff Israel said. He said the video showed Deputy Peterson doing "nothing".
The sheriff said video footage showed Peterson arriving at the building where the shooting was taking place about 90 seconds after the first shots were fired and that he remained outside for about four minutes. The attack lasted six minutes.
"There are no words. These families lost their children. We lost coaches. I've been to the funerals, I've been to the homes. ... I've been to the vigils. It's just -- there are no words."
Peterson was yet to publicly comment on what happened. Sheriff Israel said he had not given a reason for why he did not go into the building where the shooter was. It was unclear if he will face charges.
Two other deputies were placed on restricted duty because they may have mishandled tips called in to the sheriff's office over the past two years warning that the suspect, Nikolas Cruz, appeared intent on becoming a school shooter, Sheriff Israel said.
Since 2008, he said, the sheriff's office was involved in 23 calls involving either Cruz or his brother. During some of the calls -- which were handled both in person and on the phone -- deputies met Cruz's mother.
It was also reported that the surveillance footage from the shooting was not shown live, as responding officers initially thought.
According to Coral Springs Police Chief Tony Pustizzi, the footage had been rewound, and police were watching it on a 20-minute delay, leading them to believe the gunman was still in the building when he was long gone.
The revelations added to a growing list of failures and missed signs by the authorities that might have helped prevent one of the deadliest school shootings in American history.
Meanwhile, President Donald Trump has floated the idea of arming school teachers in order to avert such massacres.