I would say the supplier is culpable if the tool supplied is made for the purpose of the harm intended or if the supplier is giving the tool to the person who does the harm with the explicit intent for that person to use it for that harm. For example, giving someone an AK-47 to shoot someone or a handgun/rifle with the intent that the user shoot someone with it. If the supplier gives someone a tool to use for one legit purpose but the user uses it for a harmful purpose instead, I don't think you can blame the supplier for that. For example, giving someone a knife to cut food with, and then the user goes and stabs someone with it instead. That's entirely on the user and nobody else.