In that case, the police searched the car of a Chicago police officer who was in a coma at a local hospital. They were aiming to secure his revolver, which Chicago police were required to carry at all times.
Instead, they found evidence of a possible crime, discovered the body of a murder victim, were able to link the officer to the murder, and he was charged as a result of the warrantless search.
The Supreme Court allowed the search, saying that the officers were engaged in activities completely separate from their crime investigation/enforcement when they searched the car.
Let's pretend what conversations might be like for the two situations. "Man, sucks about Jones. Hope he comes out of it. sigh, let's go get his sidearm. I hate doing this, breaking into a guy's car like this. Oh, shit dude, isn't this the shirt that the murder victim was last seen wearing? I don't like where this might lead. But we've gotta follow up, right?"
Versus: "BMW 3 series, unlocked, left his phone in the cup holder. Let's see what else we can find."
The cynical side of me says that this is exactly why they're doing it, under the cover of doing the community a "favor". "Brilliant, Jones, just brilliant. I see lieutenant bars in your future."