Warning: This story contains content that may disturb some readers.
Surveillance video of the Pulse Night Club massacre where 49 people were killed has been made public.
The widow of the shooter, Noor Salman, is on trial on terrorism charges for her alleged role in the killings.
The video shows Mateen entering the club just before 2am and buying a ticket. He leaves for less than 10 minutes before returning to the club and opening fire.
He wanders through the club, methodically moving between rooms and firing at victims, some after they had already fallen.
At one point he drops a used clip and reloads before heading to the bathroom where many people are huddled in fear.
Police are seen entering the bar at 2:07am, less than 10 minutes after Mateen began shooting, stepping over victims and evacuating as many as possible.
At 2:37am people, some of them injured, are seen leaving the club.
The footage shows Mateen engaging with police but does not show his final moments. He was found dead more than three hours after shooting began.
Prosecutors say the video is evidence Salman aided and abetted her husband in planning the terrorist attack.
However Salman's attorney argues she had no idea of her husband's plans and Mateen decided to go to Pulse at the last minute.