Is there actual evidence of "intent of mass murder"? It seems speculative at best.
I would assume they'd need something like details of specific conversations, but I am of the opinion that the U.S. administration and courts are acting in bad faith and especially with regards to the operations of ICE.
The U.S. administration seems to not require evidence for lots of statements and especially regarding ICE (c.f. statements made about Renee Good after she was murdered).