The Police Department has the formidable responsibility of keeping New Yorkers safe from a terrorist attack. It is entrusted with significant powers and broad discretion in how to use them. It has done an admirable job in preventing violence. But last week, we were reminded that no government entity with such powers should operate free from independent oversight.

In advance of the second session of the Supreme Court's 2011 term, the Brennan Center calls attention to five cases involving important issues of access to justice, national security, and civil liberties.