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Police Blotter: E911 rules aid police in tracking cell phones

Court order lets Homeland Security obtain precise location data from T-Mobile about customer's movements in real time.

Police Blotter is a weekly News.com report on the intersection of technology and the law.

What: Minnesota man charged with alien smuggling says data from a location tap of his T-Mobile phone should not be used against him in court.

When: U.S. District Judge Paul Magnuson in Minnesota rules on January 31.

Outcome: Prosecutors can use location information.

What happened, according to court documents:
Federal prosecutors have been arguing that they should be able to track the locations of Americans through their cell phones without showing any evidence of criminal activity--in legalese, no "probable cause"--because cell-tracking technology is not that precise. Police Blotter was the first to report on this trend nearly three years ago.

In one case in Texas, for instance, prosecutors claimed in a legal brief (PDF) that: "It is true that cell-site data provides information about the location of a cell phone user. However, cell phones do not permit the detailed continuous tracking of movement..."

That was then. Now that the Federal Communications Commission's E911 requirements have led to the adoption of assisted GPS and triangulation through cellular towers, "detailed continuous tracking of movement" has become commonplace. (The Sprint Navigation and Verizon's VZ Navigator feature are two examples.)

This bring us to a case where Homeland Security's Immigration and Customs Enforcement (ICE) obtained latitude and longitude data from T-Mobile showing the location of one of the company's subscribers. ICE obtained a court order in October from a magistrate judge requiring T-Mobile to disclose the location "at such intervals and times as directed by the law enforcement agent serving this order," which would include a real-time feed as the subscriber is traveling.

To comply with E911, T-Mobile uses a GSM technology called Uplink Time Difference of Arrival, or U-TDOA, which calculates a position based on precisely how long it takes signals to reach towers. A company called TruePosition that provides U-TDOA services to T-Mobile boasts of "accuracy to under 50 meters" that's available "for start-of-call, midcall, or when idle." The company also says: "U-TDOA systems typically deliver locations to the network in less than 10 seconds from the initiation of the call, often before the voice conversation even begins."

The T-Mobile subscriber Le Guo Wu was subsequently charged with aiding and abetting alien smuggling as part of a marriage fraud scheme. Homeland Security says Wu recruited Americans to enter into sham marriages to allow Chinese citizens to enter the country. Wu allegedly offered one confidential informant $13,000.

When Wu found out location information would be used against him in court, he objected to it, saying the court order was granted based on the unconfirmed claims of informants and the location data therefore should be suppressed. A brief he filed in November said: "The affidavit submitted in support of the application for the order is largely based upon information supplied by two anonymous informants--CRI and CW. However, the affidavit fails to adequately establish the credibility and reliability of the two informants. The substance of the affidavit is really little more than a repetition of the largely uncorroborated assertions of CRI and CW."

So far he's had little luck with that argument. U.S. District Judge Paul Magnuson in Minnesota rejected the suppression request on January 31, saying there was "ample evidence" the order was reasonable. Magnuson also denied suppression requests for e-mail evidence obtained from Wu's Yahoo, Hotmail, and Gmail accounts.

In this case, police did prove they had a reasonable belief that a crime had been committed--again, probable cause--and obtained a court order signed by a judge. That means the privacy concerns in this case were not as severe as some of the earlier ones.

What's worth watching is whether the Justice Department tries to obtain similar location tracking by-the-minute-and-by-the-meter data in the future without demonstrating probable cause first. Notes Marc Rotenberg of the Electronic Privacy Information Center: "From the privacy perspective, you're going for two things, judicial review and an appropriately high standard."

Excerpt from October 25, 2007, court order to T-Mobile, which was originally sealed:
T-Mobile shall disclose at such intervals and times as directed by ICE, latitude and longitude data that establishes the approximate positions of the Subject Wireless Telephone, by unobtrusively initiating a signal on its network that will enable it to determine the locations of the Subject Wireless Telephone...

It is further ordered that pursuant to the same authority that T-Mobile shall initiate a signal to determine the location of the subject's mobile device on the service provider's network or with such other reference points as may be reasonable (sic) available and at such intervals and times as directed by the law enforcement agent serving this order...

It is further ordered, pursuant to the All Writs Act, 28 USC 1651(a), that T-Mobile shall be paid compensation by ICE for reasonable expenses directly incurred in providing the facilities and assistance described above...

It is further ordered pursuant to the All Writs Act, 28 USC 1651(a), that T-Mobile, its representatives, agents, and employee(s), unless and until otherwise ordered by the court, shall not disclose in any manner, directly or indirectly, by any action or inaction, the existence of this order...

Excerpt from January 31 court opinion by Judge Magnuson saying the T-Mobile tracking was perfectly reasonable:
Turning next to the application for the latitude/longitude order, this probable cause is based largely upon information gathered by the agents after consensually monitored calls by the CRI and CW. During the calls, Wu discussed the scheme and made identical statements to the CW and CRI. The phone numbers were interconnected and it was clear they were used for the purpose of communicating about the scheme. There is more than ample evidence in this affidavit for the request given the information gathered within control of the agents, in combination with the common facts listed earlier. They are mutually confirming facts and it all points toward probable cause.