U.S. regulators probing the May flash crash are focusing on a trading practice known as "quote stuffing", in which large numbers of rapid-fire orders to buy or sell stocks are placed and canceled almost immediately.

CFTC commissioner Scott O'Malia told Reuters on Thursday that the futures regulator was reviewing data from Nanex LLC, a trade database developer that issued a study suggesting that computer algorithms used quote stuffing to gain an edge during the May 6 crash.

The U.S. Securities and Exchange Commission, which is investigating the crash jointly with the Commodity Futures Trading Commission, is looking at quote stuffing and something called "sub-penny pricing", a person familiar with the flash crash probe said.

The Nanex study uses market graphics and playful names to illustrate quote stuffing, arguing that high-frequency trading firms do this to flood the marketplace with bogus orders to distract rival trading firms.

Investors could make trades under the false impression that those orders were legitimate, only to see liquidity disappear and the market move against them when the orders are canceled -- all in the blink of an eye.

The Justice Department's Public Integrity Section has a storied 34-year history of pursuing corruption in government and safeguarding the public trust.

That trust was breached, however, when some of the unit's prosecutors failed to turn over evidence favorable to the defense in their high-profile criminal trial of Sen. Ted Stevens, R-Alaska, who died earlier this month in a plane crash.

Now Jack Smith, a 41-year-old prosecutor with a love for courtroom work and an impressive record, has been brought in to restore the elite unit's credibility.

Before Stevens, Public Integrity's renown was built on large successes — like the prosecution of the Jack Abramoff lobbying scandal and convictions of federal and state judges, members of Congress and state legislators, military officers, federal lawmen and bureaucrats and their state counterparts over the years.

But its stumble — not disclosing exculpatory evidence as Supreme Court precedent requires — was equally large. It was so serious that Attorney General Eric Holder, one of Public Integrity's distinguished alums, stepped in and asked a federal judge to throw out Stevens' convictions.

At the time of the Stevens debacle, Smith was overseeing all investigations for the international war crimes office at The Hague in the Netherlands. He'd read about the Stevens case. Offered the chance to take over Public Integrity, he couldn't stay away.

Democratic Party Chairman Tim Kaine is defending first lady Michelle Obama's vacation trip to Spain, saying critics of her travels are trying to politicize the issue.

Kaine tells NBC's "Today" show he thinks "it's wrong" to talk critically about her trips. Critics contend they send a poor message at a time when many Americans are out of work.

Kaine said, "She's a mom." He said this was an opportunity for her to take nine-year-old daughter Sasha to a part of the world she hadn't seen before.

Kaine said President Barack Obama and Michelle Obama are "focused on being good parents." Mrs. Obama returned with Sasha to the White House late Sunday. Her trip occurred as Obama was celebrating his 49th birthday and their other daughter, 12-year-old Malia, was away at summer camp.

The family of four people killed in the crash of a Marine Corps jet in a San Diego County neighborhood two years ago sued the federal government and Boeing Wednesday.

The lawsuit was filed in U.S. District Court by Dong Yun Yoon, whose wife, two daughters and mother-in-law were killed in the December 2008 crash that incinerated two homes and damaged others in University City.

The suit accuses the military and Boeing, the aircraft's maker, of negligence and seeks unspecified damages.

The military disciplined 13 members of the Marines and Navy after the crash, which was blamed on mechanical problems and a string of bad decisions that led the pilot to bypass a potentially safe landing at Naval Air Station North Island in Coronado.

The suit claims the F-18 Hornet had "a history of warnings and system failures" related to its fuel system and never should have been cleared for takeoff.

Calls to Boeing after hours Wednesday were not immediately returned.

Court documents accuse the Marine Corps of making decisions "in violation of written military standards, which if complied with would have avoided the tragic ending."

Four members of a Korean family were killed in their home — Young Mi Yoon, 36; her daughters Grace, 15 months, and Rachel, 2 months; and her mother Suk Im Kim, 60. Kim was visiting from South Korea to help her daughter move across town and adjust to the arrival of her second child.

The pilot, Lt. Dan Neubauer, described in a statement to investigators how he struggled to control the malfunctioning jet in the minutes before the crash.

The pilot was on a training flight from the aircraft carrier USS Abraham Lincoln when he was forced to shut down one engine because of mechanical trouble. The hobbled jet was told to bypass a coastal Navy base that offered an approach over water and to instead fly inland over San Diego to Marine Corps Air Station Miramar.

Faced with expensive legal challenges, officials in the eastern Nebraska town of Fremont are considering suspending a voter-approved ban on hiring or renting property to illegal immigrants until the lawsuits are resolved.

The City Council narrowly rejected the ban in 2008, prompting supporters to gather enough signatures for the ballot measure. The ordinance, which was approved by voters last month, has divided the community. Supporters say it was necessary to make up for what they see as lax federal law enforcement and opponents argue that it could fuel discrimination.

But the council's president, Scott Getzschman, insisted the elected body was concerned about money, not about any lack of support for the ordinance. The City Council is scheduled to vote on suspending the ban on Tuesday night, a day before the city goes to court over the measure.

The city faces lawsuits from the American Civil Liberties Union and the Mexican American Legal Defense & Educational Fund. City officials have estimated that Fremont's costs of implementing the ordinance — including legal fees, employee overtime and improved computer software — would average $1 million a year.