The lawyer for a British man accused of killing his American wife and baby, yesterday asked a judge in the US to dismiss the case.
Elliott Weinstein said prosecutors had relied on "unreliable" DNA test results in affidavits and information given to the media to link Neil Entwistle to the fatal shooting of his wife, Rachel, and nine-month-old daughter Lillian Rose.
That had violated his right to a fair trial, Mr Weinstein said.
At Middlesex Superior Court in Cambridge, Massachusetts, he also opposed a request by the District Attorney's office to take a new DNA sample from the inside of Entwistle's cheek.
Prosecutor Michael Fabbri told the judge the genetic material used previously had been taken from a water bottle left in the BMW that the unemployed IT worker drove to Boston Airport before flying to the UK.
But Mr Fabbri said that a sample taken directly from Entwistle (27) was needed because the burden of proof at trial is higher than that needed to get an arrest warrant.
Entwistle denies murdering Rachel, and their daughter in January at their h ome in Hopkinton, Massachusetts.
Twenty-seven-year-old Rachel formerly taught at St Augustine's Catholic High School, in Redditch, Worcestershire.
Entwistle came face-to-face with her mother and stepfather in the courtroom for the first time since April.
Judge Peter Lauriat will rule on the motion to dismiss the case and the prosecution's request for a DNA sample at a later date, which was not given.
Mr Fabbri said investigators knew DNA taken from the water bottle was Entwistle's because it matched the parts of his daughter's DNA that did not come from her mother.
A police affidavit filed after the Briton was arrested said his DNA was on the .22-calibre pistol he is accused of using to kill the pair.
But Entwistle said an affidavit filed in support of the motion for the new sample by the chemistry head of the state's own crime lab showed the old one was unreliable.
He said that according to Gwen Pino, a scientist at the Massachusetts State Police criminal laboratory, the only reliable way to get a DNA match was with a sample taken directly from the defendant.
"We conclude that therefore what they have done is unreliable." He added: "If they want to proceed with the buccal swab then the prosecution should step forward and say it has been relying on information which it knows now not to be reliable."
He said the prosecution had been asserting from "way back" in the case that they had a DNA match for Entwistle. "What they really have is assertions of a match," Mr Weinstein added.