I'm a bit surprised that there aren't purpose limitations in the enabling legislation for the most controversial new government investigative authorities.<p>The Wiretap Act has an explicitly enumerated list of offenses for the investigation of which wiretaps may be authorized:<p><a href="http://www.law.cornell.edu/uscode/text/18/2516" rel="nofollow">http://www.law.cornell.edu/uscode/text/18/2516</a><p>The default is that a wiretap is <i>not</i> available to investigate an arbitrary crime. (Of course, there's been a lot of creep and wiretap authority has been expanded to more and more crimes.) This is based on the idea that a wiretap is uniquely and intensely invasive compared to other law enforcement techniques.<p>I don't see why that pattern hasn't been repeated with other investigative authorities. In the case of section 213 of the Patriot Act, described here, the effect of the new law was to amend 18 USC §3103a<p><a href="http://www.law.cornell.edu/uscode/text/18/3103a" rel="nofollow">http://www.law.cornell.edu/uscode/text/18/3103a</a><p>to allow for "delayed notice" when a search warrant was used. But that section authorized the issuance of warrants for "any property that constitutes evidence of <i>a criminal offense in violation of the laws of the United States</i>" (emphasis added), that is, for the investigation of <i>any Federal crime</i>. Presumably it would have been easy for section 213 to have taken a Wiretap Act-like approach and said that the delayed notice procedure was available for investigation of crimes x, y, and z, but not other crimes.<p>(I work with the author of the original article, but we haven't discussed this topic.)