( CNN ) -- A disgruntled employee shot to death the owners of a store in Boulder , Colorado , and then may have turned the gun on himself , police said Tuesday . Police found Sean Griffin , 40 , and his wife Staci Griffin , 41 , dead in a back room of the Boulder Stove & Flooring on Monday morning . Also dead was Robert Montgomery , 50 . Montgomery had a 9 mm Smith & Wesson handgun in his hand and appeared to have suffered a single gunshot wound , said police spokeswoman Sarah Huntley . The Griffins sustained multiple wounds . Montgomery told friends and wrote in a journal that he was upset over a recent change in sales commission and bonus policy at work , Huntley said . He purchased the gun on May 7 , she said . Police said Montgomery had been employed at Boulder Stove & Flooring since 2003 . A salesman and a customer were inside the store when the gunshots rang out at 11:09 a.m . They jumped in the customer 's vehicle , drove away and called 911 , Huntley said . Police arrived minutes later to find the three dead . An autopsy will determine whether Montgomery was the shooter , but Huntley said police suspect him after finding the same kind of Cor-Bon 9 mm ammunition at his house that was used in the shooting . Police said they found 13 spent shell casings around the scene of the shootings with one round still in the chamber of the gun . No rounds were left in the magazine , they said . At his home , they found a box of Cor-Bon 9 mm ammunition with 14 rounds missing . Investigators said they found a second magazine in Montgomery 's backpack loaded with 10 rounds of Eagle brand 9 mm ammunition . At his home , they found an empty box of Eagle 9 mm ammunition .
Police find three dead in Colorado store . The bodies were found at a Walmart Supercenter on the outskirts of Denver, police said. Gun purchased just days before shootings .