MONTREAL -- A pair of armed robbers got more than they bargained for when a Montreal jewelry store owner and his family fought back, throwing a tray full of acid into the thieves' faces.

Richardson Francois was a 31-year-old convicted killer with close ties to a Montreal street gang when, on Jan. 22, 2013, he and an accomplice, Jerry Theodore, walked into a jewelry store with the goal of robbing it.

Francois had pulled off a similar robbery already.

In 2012, Francois and an accomplice who has yet to be identified, were captured on a security camera posing as regular customers at a Laval jewelry store. As he would later do during the attempted heist in Montreal, Francois pretended to be interested in items in the store's display cases. In the Laval robbery, he suddenly reached out and grabbed the arms of the man who had been serving him while the accomplice headed to a back room. The accomplice threatened a woman in the back room with a machete, forced her to the floor and tied her hands behind her back. Francois then forced the man into the back room, ordering him to lie next to the woman and also tied his hands behind his back.

Security cameras recorded as Francois and his accomplice emptied the store's display cases and a vault.

But things didn't go so well in the 2013 attempted robbery.

Store owner Vijay Verma somehow disarmed Francois of his pistol and Verma's relatives emerged from a back room to help him fend off the robbers.

One of Verma's relatives picked up a tray full of nitric acid -- commonly used to clean jewelry -- and tossed it at Francois and Theodore. The acid left lifelong scars on their faces. Francois also lost 50% of the vision in one of his eyes.

Nitric acid is a highly corrosive mineral acid used in fertilizer and rocket fuel, and also used for etching steel. Even a drop will melt skin on contact.

"It was me who brought on this situation," Francois told Quebec Court Judge Helene Morin last week during a sentencing hearing for both robberies. "(Verma and his relatives) were defending themselves."

Sentence arguments are scheduled to resume on June 7.

Theodore was already sentenced in 2014 to seven years.