A purse-snatching led to the legal justification for NSA domestic spying. 

In 1976 a young woman in Baltimore, Maryland had her purse ripped off - the purse snatcher jumped into a car and took off before she could see his license plate. But Michael Smith was caught a few weeks later because the police department had tracked threatening phone calls he made to the woman. 
The case went to the Supreme Court in 1979, and it upheld Smith's conviction. 
Fast forward 35 years, and the NSA cited that case as the justification for what they call metadata surveillance of phone calls, emails and Internet use. 
- Rob Archer