It depends on what you mean by "criminal"; under environmental law, there are both negligence-based (negligent discharge of pollutants to navigable waters) and strict liability (no intent requirement, such as killing of migratory birds) crimes that could apply to this spill. I don't think anyone thinks BP intended to have this kind of spill, so the interesting question from an environmental criminal law perspective is whether BP did enough to be treated as acting "knowingly" -- the relevant intent standard for environmental felonies. This is an extremely slippery concept in the law, especially given the complexity of the systems at issue here. Litigation will go on for many years on this exact point.