New Delhi, Dec. 2 -- In 2011, the US Federal Bureau of Investigation identified Timothy Carpenter as the ringleader of a string of armed robberies in Michigan and Ohio. Instead of obtaining a search warrant to gather evidence, they chose to obtain a court order compelling his mobile carrier to hand over cell-site location data. This allowed investigators to review Carpenter's digital history-across a total of 12,898 separate location points-and map his precise movements over a four-month period. Armed with this data, the prosecution was able to place him at the scene of the robberies using his own cellphone data and secure a conviction.

The digital trails we leave behind have given law enforcement new ways to investigate crimes. In addit...