I don't know the exact regulations with new assets like crypto. It could be that pump and dump schemes are always illegal. I believe the Bitconnect people will likely end up in jail for running a Ponzi, even though it was in unregulated crypto.
With respect to jurisdiction, that does not really apply here because some of the pump and dump victims were likely from the US, and that would make a pump and dumpers actions a crime on US citizens. Someone may not get arrested in their home country but would when entering the US. In an extreme case, the US might even petition an extradition.