Seems like they want to be Martyrs to the Cause,

so give them what they want.
The two women said they researched how to pierce the steel pipe used for the pipeline and in March they began using oxyacetylene cutting torches to damage exposed, empty pipeline valves. They said they started deliberately vandalizing the pipeline in southeast Iowa’s Mahaska County, delaying completion for weeks.

Reznicek and Montoya said they subsequently used torches to cause damage up and down the pipeline throughout Iowa and into part of South Dakota, moving from valve to valve until running out of supplies. They said their actions were rarely reported in the media…
So do a proper investigation, try them, and throw their asses in cells.  And if it can be shown their organization was aware of this, or aided in any way, nail it as well.

And take note of that 'rarely reported'; gee, I wonder why...