Moreover, the surveillance was limited, both in scope and in duration, tothe specific purpose of establishing the contents of the petitioner's unlawful telephoniccommunications. The agents confined their surveillance to the brief periods during which heused the telephone booth, and they took great care to overhear only the conversations of thepetitioner himself.
This is important to note because the investigation had a narrowly tailored and significant purpose that did not extend past the reach of the investigation.