LEADING THE DAY: Sharis A. Pozen, the acting head of antitrust at the Justice Department, is leaving the agency to return to practice private law, according to a government official, The Washington Post reported. Appointed as acting attorney general for the antitrust division in August, Pozen oversaw the rejection of the proposed deal between AT&T and T-Mobile.

She will leave the agency at the end of April. The lead candidate to succeed her is William Baer, an attorney at Arnold Porter in Washington and former head of the antitrust division of the Federal Trade Commission, according to a government official.

Supreme Court GPS ruling: On Monday, The Supreme Court ruled unanimously to restrict law enforcement officers’ ability to track criminal suspects with GPS devices, The Washington Post reported. The court reversed the conviction of Antoine Jones, a suspected drug dealer, after he claimed that his Fourth Amendment rights had been violated when police placed a tracker in his vehicle to monitor his movement for 28 days.

AT&T, T-Mobile submit spectrum transfer: AT&T and T-Mobile have filed for a $1 billion spectrum transfer, part of the promised “breakup fee” that AT&T promised if the proposed merger between the companies was not successful. AT&T and T-Mobile dropped their merger bid in December, after facing opposition from the Justice Department and the Federal Communications Commission.

“This additional spectrum will help meet the growing demand for wireless broadband services,” T-Mobile senior vice president for government affairs Tom Sugrue told the Wall Street Journal.

Facebook, Twitter engineers target Google: Engineers from Facebook and Twitter have published a proof of concept plug-in for some browsers that they say shows that Google is unfairly biasing its search results. Called “Focus on the User,” the piece of code supposedly shows what results would look like if Google included results it already indexes from the social Web instead of prominently displaying the hard-coded results it gets from its own Google+ network.

Grassley criticizes LightSquared e-mails: Sen. Chuck Grassley (R-Iowa) has written to LightSquared’s Philip Falcone to ask for an explanation about why Falcone reached out to the senator’s office with what he calls questionable contact.

According to Bloomberg Businessweek, Grassley said that Falcone implied via e-mail that Todd Ruelle, who was claiming to work with LightSquared, told a Grassley staffer that a call center could be placed in Iowa if the network wins approval from the U.S. government. Grassley has been a vocal critic of the proposed satellite broadband network and of the FCC’s handling of the approval process.

In an e-mail to Bloomberg, LightSquared denied that Ruelle has worked for LightSquared, Falcone, or Falcone’s firm Harbinger Capital Partners as “an employee or a consultant.”

Megaupload: Megaupload founder Kim Dotcom will remain in custody after a New Zealand judge announced he will delay a decision on whether Dotcom can be released on bail. The New Zealand Herald reports that that the founder’s attorney has said Dotcom poses no flight risk.

The judge has said his final decision will come no later than Wednesday, Reuters reported.

Judge okays laptop decryption: A Colorado judge has ordered a woman to decrypt the hard drive of her laptop computer no later than Feb. 21, ruling that requiring a defendant to provide passcodes to their own computers does not violate the Fifth Amendment right against self-incrimination, Wired reported. Judge Robert Blackburn believes that requiring the defendant, Ramona Fricosu, to provide the unencrypted information from her hard drive is allowed under the All Writs act, which “enables the court to issue orders to effectuate an existing search warrant.”