The grieving dad of a teenage girl who died in the Florida school shooting has lashed out at a deputy who was spotted cowering outside during the massacre.

'Unbelievable,' Andrew Pollack, father to 18-year-old Meadow, wrote in a Facebook post on Saturday.

'Without question school resource officer... Scot Peterson had ample enough time to make it to the 3rd floor and prevent 6 deaths including the death of my daughter Meadow,' he continued.

Peterson resigned in disgrace on Thursday, after he was chewed out by his sheriff, Scott Israel, for failing to engage with the shooter in the deadly massacre.  

Peterson was initially the only law enforcement officer present on February 14 at Marjory Stoneman Douglas High School when the rampage that killed 17 started. 

He was seen on video hiding outside for at least four minutes during the shooting, Broward County Sheriff Scott Israel said.

'Words can't describe how upset and angry I am,' Pollack continued.