Watch live: Texas Gov. Greg Abbott to address Uvalde school shooting investigation at 3:30 p.m. CT

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Editor's note: This press conference is over. For our coverage, read more here. Watch the press conference here.

Gov. Greg Abbott is set to address the public from Uvalde on Friday about the Robb Elementary School shooting this week that left 21 people dead including 19 students and two teachers. Abbott's appearance comes hours after state law enforcement said local police overseeing the response to the massacre made crucial mistakes.

Police officers did not act sooner to stop the 18-year-old gunman because a supervising officer at the scene wanted to wait for backup and equipment, said Steven McCraw, director of the Texas Department of Public Safety. By the time a specialized team of federal officers arrived and entered the school — they had to get keys from a janitor to open locked classroom doors — more than an hour had passed since the shooter arrived at the school, McCraw said.

"Of course it was not the right decision,” McCraw said. “It was the wrong decision."

McCraw also provided a more detailed timeline of what transpired that day, including 911 calls from teachers and students trapped inside with the gunman.

In the days after the massacre, DPS officials and Abbott put out conflicting information, including whether the shooter encountered a police officer employed by the school district before charging through a back door. Authorities later said there was no officer on campus when the shooter arrived and that he went into the building unopposed.

A day after the shooting, Abbott had praised law enforcement for their role in the shooting.

"It could have been worse. The reason it was not worse is because law enforcement officials did what they do," he said at the time.

Watch Abbott live courtesy of KXAS (NBC DFW) starting at 3:30 p.m. CT.