On Monday, KVUE and its news partners at the Austin American-Statesman exclusively obtained surveillance footage from inside Robb Elementary School on the day of the May 24 shooting. The footage shows that multiple officers were inside the building with rifles and at least one ballistic shield, 19 minutes after the gunman arrived. They didn't enter the classroom the shooter was inside for nearly another hour. Investigators believe this will prove to be a significant development as it indicates they had more than enough firepower and protection to enter that classroom before they actually did. Authorities have since developed their most extensive timeline yet since the shooting, in which an 18-year-old armed with an AR-15 walked into the school, killing 19 students and two teachers. Much of this new information is expected to be presented at a Texas Senate hearing on Tuesday, the first of two consecutive days at the Capitol where members of the public can address lawmakers. MORE: https://bit.ly/3O8iMSx ►Subscribe: https://on.wtsp.com/youtube ►Website: https://www.wtsp.com/ ►Facebook: https://facebook.com/10TampaBay ►Twitter: https://twitter.com/10TampaBay