The alleged crime took place in the 100-block of 1st Avenue of the town at around 11:10 p.m. on June 28.
Two people reported being approached by a black truck and then a man exited the vehicle and demanded they give him items they were carrying, according to a police report.
A second man in the suspect truck brandished a gun during this offence, Humboldt RCMP said.
Police believed there were several people in the suspect vehicle at the time, who made off with some goods eastbound of Leroy. No injuries were reported.
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The truck is described as a 2008-2010 model Ford F350, with blue LED headlights, and was dirty in appearance with no licence plate.
The suspect who exited the vehicle is described as Caucasian, in his mid-30s, around five-foot-10, with a medium to stocky build and dirty blond hair, shorter than collar-length.
Police are cautioning the public not to approach the suspect.
Anyone with information is asked to contact Humboldt RCMP at 306-682-2535 or Crime Stoppers at 1-800-222-8477.
Leroy is approximately 150 kilometres east of Saskatoon.