[2] In 1997, Nelson wrote the court's opinion in Montana v. Siegal ruling that police usage of thermal imaging technology to find a marijuana growing operation required a search warrant, four years before the U.S. Supreme Court ruled similarly in Kyllo v. United States in a decision written by Justice Antonin Scalia.

[2] In a 2009 child custody case between two same-sex partners, Kulstad v. Maniaci, Nelson gained attention from the media and civil rights groups for his concurring opinion that stated: Naming it for the evil it is, discrimination on the basis of sexual orientation is an expression of bigotry.

It cannot be justified; it cannot be legalized; it cannot be constitutionalized ... Lesbian and gay Montanans must not be forced to fight to marry, to raise their children, and to live with the same dignity that is accorded heterosexuals.

That lesbian and gay people still must fight for their fundamental rights ... speaks, in unfortunate clarity, of a prevalent societal cancer grounded in bigotry and hate.

Nelson's ruling made it easier for prosecutors to introduce evidence against defendants by discussing past crimes, behaviors, and events.