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... This type of data is typically used to aid investigations into potential crimes. In this case, the US sought such data to see whether suspected violent gang members could feasibly be connected to a string of homicides, shootings, and vehicle thefts over a 14-month period.

Tower dumps can include information on all connections to that tower within windows ranging from ten minutes to one hour. As such, the data returned from these requests would also include that of various individuals who are not of interest to the FBI's investigation.

United States Magistrate Judge Andrew S Harris denied the feds' four-warrant request for tower dumps in February, citing incompatibility with the Fourth Amendment.

Fourth Amendment rights under the US Constitution protect citizens from unreasonable searches and seizures.

The FBI sought the data from towers across nine locations "to help identify or eliminate suspects," and this data would include phone numbers, unique device identifiers, the dates, times, and duration of each connection, and the types of communication transmitted via the tower, such as SMS or phone call.

Citing case law, Judge Harris denied the FBI's request in Mississippi. He wrote in his ruling [PDF]: "For starters, while the government has some idea of who may have been involved in one or more of the crimes --" the affidavits supporting the warrant applications list seven potential suspects -- the government has not presented probable cause to believe that any particular individual committed any of the specific crimes described.

"The warrant applications also arguably present probable cause to believe that the searches will reveal the location data of some unknown perpetrators of the crimes ...

But this is not enough. If the court were to issue the warrants, it would be authorizing the government to search the data for every cellular device (including cell phones) of every single individual near the crime scenes without a showing of probable cause as to each individual.

"Stated another way, the government is essentially asking the court to allow it access to an entire haystack because it may contain a needle. But the government lacks probable cause both as to the needle's identifying characteristics and as to the many other flakes of hay in the stack." ...