San Diego: A woman once convicted of killing her husband with arsenic to pay for breast implants was cleared after new tests showed no traces of poison.

Prosecutors who were preparing for Cynthia Sommer's second trial found that previously untested samples of Marine Sergeant Todd Sommer's tissue showed no arsenic. Earlier tests of his liver, presented at the woman's first trial, found levels 1,020 times above normal.

A recently retained government expert speculated that the earlier samples were contaminated, prosecutors wrote in a motion filed in San Diego Superior Court. The expert said he found the initial results "very puzzling" and "physiologically improbable".

San Diego County District Attorney Bonnie Dumanis told reporters on Thursday there was no proof of contamination but offered no other explanation. She said she didn't know how the tissue might have been contaminated.

"The bottom line was, 'Was there arsenic in Mr Sommer causing his death?' Our results showed that there was," Dumanis said.

Sommer was released from jail on Thursday night after two years and four months' incarceration in suburban Santee.

"Hi, honey. I love you," she told her daughter on her cell phone. "I can't wait to see you. I miss you."

At her trial, prosecutors argued that Sommer used her husband's life insurance to pay for breast implants and pursue a more luxurious lifestyle.