On Wednesday, February 14, a 19-year-old male entered a building of his old high school, climbed to the third floor and pulled the fire alarm. As students began to flood the hallways, he began to open fire upon them killing 17 and injuring a dozen more.

Police responded to the scene quickly and only had a few short minutes to decide how to approach the deadly events unfolding. In order to give themselves a better idea of what they were dealing with, they gained access to the school's surveillance system.

Closed-circuit surveillance cameras helped police track the gunman's movements through the school that day, giving authorities a way to time stamp when the gunman entered the school, his movements as he moved from the third floor, to the second floor and back again, firing his AR-15-style gun the whole time, and, finally, when he ultimately left the school.

The footage, however, was not as helpful in real-time as they had hoped it would be, as the surveillance system played on a 20-minute delay. Officers, FBI and SWAT team members were operating blind as they moved into the school, escorting students out and helping those who were wounded.

Footage taken by students inside the school building at the time of the incident will also help police put together a comprehensive time line of the shooting. Several students used smartphone applications Snapchat and Instagram as well as the camera on their smartphones to document the events unfolding around them.

The footage is disturbing, but shows the actions of teachers and students in real-time as the shooter made his way in and out of classrooms and through hallways. Students also shared video of police entering classrooms and auditoriums to escort students out of the building when the grounds had been deemed "safe."

Here's the timeline of events according to Broward Sheriff Scott Israel:

2:06 PM: Uber picks up the suspect.

2:19 PM: Uber drops the suspect off at Stoneman Douglas High School.

2:21:18 PM: Suspect enters the east stairwell of Building 12 with rifle in a black, soft rifle case.

2:21:30 PM: Suspect exits stairwell with rifle removed from the rifle case.

2:21:33 PM: Suspect has rifle ready and begins shooting into classrooms. Suspect then takes the west stairwell to the second floor and shoots into a classroom there.

2:24:39 PM: Suspect takes takes the east stairwell to the third floor.

2:27:37 PM: Suspect enters the third floor stairwell, drops the rifle and backpack and runs down the stairs.

2:28:35 PM: Suspect exits the building and runs west toward the tennis courts and then heads south.

2:29:51 PM: Suspect crossed the field and runs west with others who are fleeing the area.

2:50 PM: Suspect arrives at a Walmart, goes inside and purchases a drink at the Subway inside.

3:01 PM: Suspect goes to McDonalds, sits down for a short time and then leaves on foot.

3:41 PM: Suspect is detained at 4700 Wyndham Lakes Dr., Coral Springs by an officer from Coconut Creek PD. A show up is conducted at that location by BSO homicide detectives. He is positively identified and taken into custody.