Cynthia Sommer

Cynthia Sommer talks to reporters after being released from jail after the murder case against her was dropped. (Denis Poroy / Associated Press / April 18, 2008)

SAN DIEGO -- A federal judge Thursday dismissed a lawsuit by a Marine widow who claimed she was convicted of murdering her husband because investigators and prosecutors unfairly focused on her libertine lifestyle.

After Sgt. Todd Sommer, 23, died mysteriously in February 2002, his widow, Cynthia, had her breasts enlarged, had sex with three other Marines, held raucous parties and participated in a thong and wet T-shirt contest in Tijuana.

In November 2007, a Superior Court jury convicted Cynthia Sommer of murdering her husband, largely on the basis of forensic evidence showing traces of arsenic in his body.

But the trial judge set aside the verdict and ordered a new trial, ruling that Sommer's defense attorney should not have allowed prosecutors and prosecution witnesses to talk about Sommer's behavior in the months after her husband collapsed and died in their apartment at Marine Corps Air Station Miramar.

In April 2008, as prosecutors were preparing for a retrial, the district attorney moved to dismiss the case, noting that new scientific scrutiny had undercut the assertion that the sergeant was killed by arsenic poisoning.

Sommer's appellate attorney had argued that prosecutors erred by not having additional tests done to rule out contamination in the samples that had found arsenic.

By the time she was freed from jail, Sommer had served 876 days behind bars.

Sommer had initially been convicted of murder and murder for hire, which carries a mandatory life sentence.

At the district attorney's request, the judge dismissed the case "without prejudice," giving prosecutors the option of refiling charges, although they never were.

Sommer, now 39, filed a federal lawsuit in 2009 seeking $20 million in damages on the grounds that Naval Criminal Investigative Service agents failed to conduct a decent investigation once they learned of her partying lifestyle.

U.S. District Judge Cathy Ann Bencivengo threw out Sommer's lawsuit on Thursday. The evidence "does not support plaintiff's theory that NCIS agents fabricated evidence or knowingly withheld evidence ... because they wanted to punish her for her lifestyle choices."

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tony.perry@latimes.com

Twitter: @LATsandiego