Parkland massacre gunman Nikolas Cruz was able to escape the Florida campus undetected because security guards were watching surveillance footage on a 20-minute delay.

The confusion caused police to believe that Cruz was still on school premises, even though he had already left and was on the way to Subway and McDonald's.

Police searched for the gunman for 26 minutes using security cameras before realizing he wasn't inside Marjory Stoneman Douglas High School.

In footage reviewed by the Sun Sentinel officers can be heard saying that they are monitoring him on camera and he's moved from the third to second floor.

Footage shows Nikolas Cruz, 19, making his way towards a McDonald's, on Wednesday, about an hour after the shooting

Cruz reportedly did not purchase anything inside the McDonald's and was detained approximately 40 minutes after

Another cop replied that they were on the second floor and couldn't see Cruz, because he managed to get away unnoticed after his shooting spree where he killed 17 people.

Officers realized from the footage that Cruz dropped his rifle and fled the scene at around 2.28pm and was caught by police an hour later.

Nikolas Cruz was able to leave Majory Stoneman Douglas campus without being detected due to a 20-minute delay on the security cameras

The tapes confirm a malfunction in the cameras as an officer can be heard saying: 'It's about a 20-minute delay they're following him on video, on the camera.

'They have him exiting the building, running south.'

Deputies from the Broward County Sheriff's Office reportedly arrived at the campus just as Cruz was escaping.

There is speculation over whether they responded to the right building at first but this is unable to be determined by the tapes.

Broward Sheriff Scott Israel said at a press conference Wednesday that investigators were 'examining' the tapes and other evidence to see if deputies immediately entered the school upon their arrival.

Criminal Justice Professor Pete Blair said he had never heard of a 'camera delay' problem before.

Officers realised from the footage that Cruz dropped his rifle and fled the scene at around 2.28pm after killing 17 people and was caught by police an hour later.

He added that the 'good information' you think you have is going to slow the process down because it turns out to be misleading.

Coral Springs Police Chief Tony Pustizzi confirmed that the surveillance tapes offered to police by the school were 'delayed 20 minutes and nobody told us that.'

He told the Sun Sentinel: 'It made it harder to identify where the guy was.

'Somebody would say "he's on the second floor", and we had guys on the second floor saying "we're on the second floor, we don't see him", that's when we figured out there's a tape delay.'

He added: 'Once we found that out we were able to adjust.'