Multiple officers were inside Robb Elementary School armed with rifles and at least one ballistic shield by 11:52 a.m. on May 24, but they didn't breach a classroom door and take out the gunman who killed 19 children and two adults for nearly an hour, according to documents reviewed by the Austin-American Statesman. 

The new details shed light on the shifting timeline that law enforcement has provided about the response to the third-deadliest school shooting in U.S. history.

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