The first 911 calls reporting shots fired came in at 12:11 p.m. Wednesday at the Citibank Center in Brandon, a suburb of Tampa.

According to the Hillsborough County Sheriff's Office, the driver plowed a small sedan over medians and grass, crashed through a secure fence, and stopped in a courtyard where employees were eating lunch.

He got out with a rifle and fatally shot a woman seated outside, then moved into the building toward the cafeteria. At 12:15 p.m., an armed Citi security guard confronted him there and exchanged gunfire; the suspect was wounded and taken to Tampa General Hospital, where he died.

Sheriff's officials said the guard stopped what could have been a far deadlier rampage. Chief Deputy Frank Losat said there was 'absolutely' potential for further violence and credited the guard directly: 'kudos to that security guard.'

Sheriff Chad Chronister said the suspect appeared intent on killing as many people as possible, and that the actions of the security team and hundreds of deputies stopped him before he could harm anyone else.

The guard himself was injured in the exchange, and at least four other people were treated for non-life-threatening injuries.

The sheriff's office released body camera footage from 12:16 p.m. showing an officer sprinting across the campus, shouting that the subject was in the cafeteria and 'possibly down,' then moments later that the 'shooter is down.'

More than 365 sheriff's deputies, SWAT teams, fire rescue crews, and state and federal partners responded, evacuating roughly 3,200 employees from the multi-building complex in about two and a half hours.

Employees described terrifying moments of sheltering as the attack unfolded.

A cafeteria worker who asked not to be named said her first instinct was to call her mother so someone would know if something happened to her, and she hid with five others until police arrived, hearing a crying woman describe believing the shooter had been near her earlier hiding spot.

Doug Merritt told The Associated Press his son fled the building after hearing gunshots and spent roughly an hour unreachable due to a poor connection.

Officials have not released the names of the gunman or the victim, nor a possible motive; FOX 13 Tampa Bay reports detectives spent Wednesday night questioning witnesses and that it remains unclear whether the two knew each other.

Citi Chair and CEO Jane Fraser confirmed the victim was a company employee, writing that her heart goes out to the colleague's loved ones and that she is grateful to the security team whose actions 'prevented this awful day from being even worse.'

She said the Tampa campus is secure, that additional security is being added at other sites as necessary, and that counseling and other resources are available to employees; a company spokesperson said staff are not expected to work Thursday.

Investigators continue working to establish a motive, and authorities are expected to release more detail as the witness interviews conclude.