He has recently enacted a law to trace and help thousands of victims caught up in drug violence and other crimes.

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Whatever their little differences are, they all go back and trace their sources to shariah law.

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It can takes weeks or even months, if law enforcement is lucky, to trace a gun back to its origin.

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Difficult to trace, let alone prosecute, they are the most likely to be breaking the law and employing illegal immigrants.

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Still, law enforcement, regulators and financial institution have expressed worries about the hard-to-trace attributes of virtual currencies, helping trigger this week's move from the Treasury's Financial Crimes Enforcement Network, or FinCen.

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The gaps in the federal database trace back to a 1997 U.S. Supreme Court decision that struck down part of a law requiring states to report mental-health records, ruling that states could share such records as they wished.

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In addition to scrutinizing images of surveillance cameras in the area, the FBI likely was issuing subpoenas for records from cell towers in the area to isolate and trace calls from around Copley Square at the time of the blasts, according to a former federal law enforcement official who now works in the intelligence community.

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