06/19/2015 12:06 EDT | Updated 06/19/2016 05:59 EDT

Toronto police offer $50K reward 35-year-old murder of Brinks guard

Toronto police have doubled a reward for information related to the shooting death of a Brinks guard who was ambushed while making a bank delivery 35 years ago.

Investigators are now offering $50,000 for information that leads to the arrest and conviction of the person or persons responsible for the death of Larry Roberts on April 24, 1980.

"Investigators believe that with the passage of time, someone may feel remorse and may want to come forward with information that they have been keeping to themselves for the past 35 years," homicide Det. Mary Vruna told reporters on Friday.

Around 1:30 p.m. the day of the shooting, Roberts and two other guards from Brinks Canada Ltd. were delivering "a substantial amount of money" to a TD Bank at Agincourt Mall at 3850 Sheppard Avenue East.

Three gunmen "ambushed" Roberts and another guard, Theodore Montgomery, as they entered the southeast entrance of the plaza, Vruna said. One gunman shot Roberts in the chest at close range. A second gunman shot Montgomery.

The two gunmen grabbed bags of money and, along with the third gunman, ran toward the nearby public library branch. The three ran out the library's rear entrance and were seen getting into a light-green, full-size, late-model American car.

The suspects made off with $178,000 in cash.

Montgomery made his way into the bank, where he was assisted by customers, while Roberts remained on the ground unconscious. Both were transported to hospital, where Roberts later died. He was 29.

At the time of the homicide, investigators gleaned enough information about one of the suspects to issue a composite sketch. On Friday, police released an updated version of the sketch to show what the suspect may look like this year.

The three suspects are believed to have ties to Ontario, Quebec and Saskatchewan, Vruna said, and police believe they committed similar crimes either before or after Roberts's murder.

"The suspects in this case were sophisticated and knew what they we redoing," Vruna said, pointing to the fact that they were at the plaza at the time of the Brinks delivery. This suggests they had "done some research," she said, and were familiar with the timing of deliveries to the bank branch.

Anyone with information about the case is asked to call Det. Mary Vruna at 416-808-7409 or Crime Stoppers at 800-222-TIPS.