Newly released surveillance footage appears to support the Broward sheriff's account that a campus deputy rushed to the Parkland high school building where a mass shooting was unfolding — but never entered to engage the gunman.

Authorities on Thursday released the video showing Deputy Scot Peterson and a civilian security guard hurrying on a golf cart to Building 12 at Marjory Stoneman Douglas High in the initial moments of what became Florida's deadliest school shooting.

Watch the full, unedited video here:

But as shooter Nikolas Cruz remained inside for another four minutes — killing 17 people and wounding 15 — Peterson appeared to remain around the southeast corner of the building.

"The video speaks for itself. His actions were enough to warrant an internal affairs investigation, as requested by Sheriff Scott Israel on Feb. 21. After being suspended without pay, Peterson chose to resign and immediately retired rather than face possible termination," the department said in a brief statement with the video's release.

Read More: Citing "strong public interest," a Broward judge last week ordered public release of the four video clips from the surveillance system at Marjory Stoneman Douglas High. The 27-minute video file does not show the carnage inside Building 12, and only provides a limited snapshot — mostly focused on Peterson — of the overall law-enforcement response to the mass shooting.

The release of the video stemmed from a lawsuit filed by the Miami Herald, the South Florida Sun-Sentinel and other media outlets against the Broward Sheriff's Office and the Broward County school district, seeking release of video clips so that the public can "be given the first-hand opportunity to review and evaluate the video and the actions of its government officials."

Cruz, 19, is awaiting trial on 17 counts of first-degree murder. Prosecutors are seeking the death penalty.

Exactly how the Broward Sheriff's Office responded in the initial moments of the Feb. 14. massacre has been the focus of extensive national criticism. BSO policy calls for deputies to engage an active shooter and eliminate the threat, but does not explicitly say an officer "must" enter a building.

Peterson, shortly after he resigned, insisted that he followed BSO training, establishing a "tactical position" because he believed the gunfire was coming from outside the building. His lawyer said that an eye witness and the video from the school's surveillance system "will exonerate him of any sub-par performance."

His attorney, Joseph DiRuzzo, could not be reached for comment Thursday.

The video clip begins shortly after gunfire erupted, with Peterson and civilian security monitor Kelvin Greenleaf walking with purpose outside an administration building, clearly alarmed by sounds. When the fire alarm is triggered — apparently by the smoke of the gunfire — the two begin running, get into a golf cart and speed toward Building 12.

The angle of the remaining footage shows the two pull up to the southeast corner of Building 12 as what appears to be a group of students — the images are blurred under orders from the judge — seem to be moving about frantically on a lawn. Peterson and Greenleaf can be seen waving, then the school officer assumes a position that is partially obstructed by a pole.

The footage apparently shows Peterson remaining in that area for the next 20-plus minutes of the clip. "Do not approach the 12 or 1300 building, stay at least 500 feet away," a panicked Peterson shouted as people screamed in the background, according to radio recordings released last week.

Greenleaf appears to leave the view. Other officers show up, though it is not clear from the video whether they are BSO or Coral Springs officers, and students are eventually led out of the building.

The footage does not show Cruz, who shot up the inside of the school for about six minutes. It took officers 11 minutes to finally enter the building from the time the shooting was first reported.

BSO initially resisted release of the video, but at a hearing in the media lawsuit last week, changed course and agreed the footage should be made public. The Broward State Attorney's Office and the school district asked that it be kept secret, but decided against appealing the judge's ruling.