THE RECENT EXPANSION of Google’s Timeline feature can provide investigators unprecedented access to users’ location history data, allowing them in many cases to track a person’s every move over the course of years, according to a report recently circulated to law enforcement.

“The personal privacy implications are pretty clear but so are the law enforcement applications,” according to the document, titled “Google Timelines: Location Investigations Involving Android Devices,” which outlines the kind of information investigators can now obtain.

The Timeline allows users to look back at their daily movements on a map; that same information is also potentially of interest to law enforcement. “It is now possible to submit a legal demand to Google for location history greater than six months old,” the report says. “This could revitalize cold cases and potentially help solve active investigations.”

The report was written by a law enforcement trainer, Aaron Edens, and provides detailed guidance on the wealth of historic location information available through Google Timeline and how to request it. A copy of of the document was obtained by The Intercept.

The expansion of Google’s Timeline feature, launched in July 2015, allows investigators to request detailed information about where someone has been — down to the longitude and latitude — over the course of years. Previously, law enforcement could only yield recent location information.

The 15-page document includes what information its author, an expert in mobile phone investigations, found being stored in his own Timeline: historic location data — extremely specific data — dating back to 2009, the first year he owned a phone with an Android operating system. Those six years of data, he writes, show the kind of information that law enforcement investigators can now obtain from Google.

The document also notes that users can edit or delete specific locations in their history, or an entire day, stressing the importance of preservation letters for criminal investigators involving Android phones. “Unfortunately, Google has made it very easy to delete location history from a specific date,” he wrote.

There is no indication data is recoverable from Google once it has been deleted by the user, the report says.

Location data is only stored in users’ Google accounts if they enable the feature. Individual Android users can turn it off, but users often don’t.

The ability of law enforcement to obtain data stored with privacy companies is similar — whether it’s in Dropbox or iCloud. What’s different about Google Timeline, however, is that it potentially allows law enforcement to access a treasure trove of data about someone’s individual movement over the course of years.

The report also advises investigators to remember there is a significant amount of other information retained by Google.

“Consider including Gmail, photos and videos, search history, contacts, applications, other connected devices, Google Voice and Google Wallet, if they are relevant to the investigation,” the report suggests. Investigators are also advised to include a non-disclosure order with their search warrants for Google data, which prevents the company from notifying the account holder that their data is being provided to law enforcement.

It’s impossible to know how many of these requests for historic Timeline location information have been made by law enforcement, since Google does not specify what types of requests it gets from law enforcement. Google’s transparency report provides information on the number of requests received from law enforcement, and the most recent requests go up to the end of 2014 and do not cover the time period after the expanded Timeline was launched. (In the first half of 2014, Google received 12,539 criminal legal requests in the U.S. and in the second half it received 9,981.)

The major barrier law enforcement faces is that Google does not provide any additional advice or help on deciphering data, once it is turned over under subpoena or warrant. “Based on conversations with other law enforcement investigators and prosecutors, they have resisted attempts to bring them into court to discuss the issue,” Edens wrote.

“Google does not provide expert witness testimony,” Edens said in response to The Intercept’s questions, noting that this is a similar practice to that of other companies, like Facebook. His report, he added, was written to help law enforcement in the absence of assistance from Google.

“Google has always been wary of any perceived cooperation with law enforcement, even before [Edward] Snowden,” he said.

“We respond to valid legal requests, and have a long track record of advocating on behalf of our users,” a Google spokesperson told The Intercept.

Research: Micah Lee

Update: November 9, 2015

In an email, the Google spokesperson notes that the company requires a warrant to obtain detailed user data such as that available in Timeline. “A subpoena,” the spokesperson writes, “is not and has never been sufficient to get it.” The article has been updated to reflect this.