SCOTUSBlog: Symposium: A defense of the doctrine by David LaBahn, president and CEO of the Association of Prosecuting Attorneys (with links to other articles in the same vein):
As people have become more reliant on cellular devices, so too has law enforcement become more reliant on using the information contained on, or generated by, these devices to investigate crime. Increasingly, routine law-enforcement practice has been to request incidental-transmittal-cellphone data from cell-service providers. The Washington Post recently reported that requests under 18 U.S.C. § 2703(d) have increased dramatically since 2014 in the District of Columbia alone. AT&T received over 75,000 requests from law enforcement between 2015 and 2016. Inevitably, the collection of such data by law enforcement has led to the introduction of the data as evidence in criminal trials.
In Carpenter v. United States, the government used historic cellphone-location-site information (CLSI), obtained pursuant to a Section 2703(d) order, for a period of 127 days to place the defendant, Timothy Carpenter, within a half-mile to two-mile area near the scene of the multiple robberies for which he was charged and later convicted. Carpenter filed an appeal claiming that the collection of his call location under Section 2703(d) violated his Fourth Amendment protection against unreasonable searches. His appeal was denied by the U.S. Court of Appeals for the 6th Circuit, and the Supreme Court agreed to review his case.