It was a shock absorber, which is a cylinder filled with oil and compressed gas. It seems to me like you don't pick a shock as random bullshit because you likely know it's an explosion risk covered in warning labels. They come with instructions on how to drill them before disposal. That'd be my guess as to why they're going with such motivated charges.

Or, the victim's family is connected to the judiciary system

Or, because it's the USA, assigning a perpetrator is the only way to get someone's health insurance to pay out. Ever hear of them suing themselves? It's to force insurance.