Disturbing video shows a shirtless gunman moments before he opened fire at a Citibank campus near Tampa, Florida, killing one woman and injuring four others in what authorities believe was a targeted attack.

The suspect allegedly drove his vehicle through a fenced-off area at the corporate campus before launching the shooting. Bank employees were eating lunch outside when the gunman began firing.

Investigators believe the attacker intended to kill as many people as possible, but a security guard intervened and stopped him before the violence could escalate further.

More than 3,200 people were on the bank’s campus at the time of the shooting, raising serious questions about how many additional lives could have been endangered had the attacker not been stopped.

“This was a tragic situation where a victim was killed by an individual who was intent on killing as many people as possible,” Hillsborough County Sheriff Chad Chronister said in a statement.

Four other victims suffered injuries that were not considered life-threatening and were transported to a local hospital for treatment.

The scale of the emergency response reflected the seriousness of the attack. More than 400 law enforcement officers responded to the scene to secure the campus and protect those who were there.

Authorities are investigating the circumstances surrounding the shooting, including the suspect’s alleged motive and the events leading up to the attack. The reported intervention by the security guard may have prevented an even greater loss of life.