Here is the opinion in In the Matter of the Civil Confinement of Johnson.

The court’s syllabus:

The state does not have jurisdiction pursuant to Public Law 280 to civilly commit an enrolled member of a federally recognized Indian tribe as a sexually dangerous person under the Minnesota Commitment and Treatment Act.  But in the absence of express congressional consent, the state does have jurisdiction to civilly commit an enrolled member of a federally recognized Indian tribe as a sexually dangerous person under the commitment and treatment act where, as here, federal law does not preempt state jurisdiction and exceptional circumstances exist.