A lot of criminals use the wrong cartridges in the firearms they process.
Sounds like some clown loaded a rimless round half@$$ed backwards into the mag and then somehow got the magazine into the gun. When told to pull back the slide to load said round which is where it got as far as it was going to go. The bullet would have been a far gentler death than what these bitches did to that poor baby.
A funny scene on figuring out which bullet went into which gun was “Going in Style” with George Burns, Art Carney and Lee Strasberg.