In a way, I see why the judge threw out the charges like he did. Firing blindly like the officer did doesn't fall under involuntary manslaughter, it falls under the umbrella of murder. Involuntary manslaughter is the wrong charge, because it usually means that some lesser reckless behavior was being engaged in that accidentally ended up killing someone.
This is the key part of the Illinois murder statute:
The facts of the case falls pretty squarely into the scenario provided in 2. Charging first-degree and second-degree murder would have been appropriate, not involuntary manslaughter. Calling his behavior reckless is appropriate in a common usage sense, but the circumstances seem to describe a situation that go beyond reckless into the realm of what is known as "depraved indifference". Depraved indifference is the way that you get to press for murder charges against someone who fires blindly into a crowd, since the random nature of the shooting takes away the layer of intent.
Also, I'm not at all a lawyer, but the bit about double jeopardy sounds like bullshit to me. The charges were thrown on the basis that the homicide was not involuntary, not because they couldn't meet the other standards of the crime that would place it as a lesser included offense to actual murder charges. It probably would prohibit further charges in the case of the latter, but not necessarily in the former. I would think anyway (again, not a lawyer).
EDIT:
To be fair, the judge threw out the case because they had undercharged the officer. Involuntary manslaughter has a definition that doesn't stretch to include something this reckless, and the prosecutors fucked up majorly by filing it this way.
