The murderer most likely would not. If some teenager took his parents' weapon while they were away at work, and replaced it before they got home, this tactic might actually find that out. It's reaching, but they don't have much else with which to work. I'm a little concerned they're so sure it's a Glock, though. Tell-tale signs might be a bulge on the casing due to the casing being slightly unsupported towards the bottom rear of the chamber, or the mark left by the firing pin, but there are multitudes of .40 caliber pistols, and some of those casings are going to look similar from whatever weapon they're fired.
...and I forgot to mention, Glock barrels usually have a right-hand hexagonal twist. I believe most other .40 caliber weapons put a left-hand twist on the bullet itself. Probably more likely to gather this information from the bullet than the casing.