A video taken shortly before police shot and wounded a 15-year-old boy early Thursday morning shows him inside a Mississauga, Ont., pizza outlet wrestling with an employee for control of the gun he brought with him.

A teen was rushed to Sick Kids Hospital in serious condition after he was shot by an officer outside the Pizza Pizza at Britannia and Creditview roads shortly afterward.

Peel Regional Police had been called to the plaza just before 2 a.m. after reports of three young males involved in a robbery at a gas station, Jason Gennaro, spokesperson for the province's Special Investigations Unit, told reporters at the scene.

The Special Investigations Unit has taken over the investigation into a police shooting in Mississauga, Ont., early Thursday morning. (Tony Smyth/CBC)

Two of the males fled before police arrived, Gennaro said. But the other remained and allegedly tried to rob another business.

Employees at the Pizza Pizza told CBC Toronto that it was the business targeted, with one worker saying that she felt uneasy when a teen wearing a grey sweatshirt walked in.

She moved away and another employee went to serve him.

Footage of the encounter, provided to CBC Toronto by one of the pizzeria's employees, shows the teen speaking to the employee. The pair are separated by a counter and a computer that acts as a cash register.

Fighting over the gun

Moments later, the teen pulls out a gun from the pocket of his sweatshirt. He lifts it over the register and holds it roughly 10 centimetres from the employee's face.

On the video, the employee makes a grab for the muzzle of the gun, his arms stretching over the computer screen as he and the teen wrestle for control of the weapon.

The employee loses his grip and the pair back out of the video frame on opposite sides.

It's unclear what happens next.

Employees at the pizza shop told CBC Toronto that the employee in the video had not come in to work Thursday night. And no one from the company's corporate communications could be reached to speak about what sort of training workers are given to prepare them for attempted robberies or other violence on the job.

Police shooting

The teen is alleged to have tried to enter three separate cars with people inside them after the attempted holdup, according to the SIU. Officers found the teen outside a bank in the plaza.

"There was an altercation and one police officer discharged a firearm," an SIU news release said.

The SIU has taken over the investigation into the shooting. The provincial agency probes incidents involving police that result in serious injury or death or involve allegations of sexual assault.

Six investigators and two forensic investigators have been assigned to the case, Gennaro said.

Gennaro said investigators will look for video surveillance footage from businesses at the plaza, but also appealed for witnesses to come forward.

A woman who alleges the teen entered her car told CBC Toronto that she had been the person to call 911. She provided a video of herself speaking on the phone as police arrive, which includes the moment at which the teen was shot by an officer.

Meanwhile, Peel Regional Police have yet to catch up to the two males who fled the scene. It is believed they fled in a grey vehicle, Gennaro said.