Datuk Seri Anwar Ibrahim's co-counsel Ramkarpal Singh submitted that the prosecution had failed to explain the source of the contributor of the third DNA in the "intimate samples" during the Opposition leader's sodomy trial.
He argued that two samples taken from Saiful's anus and a Good Morning towel found in Anwar's lock-up on the night of July 16, 2008 have the third party's DNA.
Ramkarpal said the presence of third party's DNA could only happened if Saiful had a sexual relationship with a man or that someone else had came into contact with the samples taken from the complainant.
"Only two ways (third party's DNA) this can happen. First, if he (Saiful) had a sexual relationship with a man who ejaculated inside him leaving his DNA there.
"Or someone else had come into contact with the sperm after it was extracted," he argued before a three-man panel chaired by Justice Balia Yusof Wahi with Justices Aziah Ali and Mohd Zawawi Salleh.
He said the defence do not know the identity of the third party contributor.
"There is certainly some form of tampering as he (Saiful) himself said that he is not homosexual.
"It cannot be a coincidence for a same person's DNA to be found on the different items," he said.
He said the possibility of retired investigating officer Supt Judy Blacious Pereira to have contact with the samples could not be excluded due to him being a custodian of those items for a longer time.
"It is not for us to speculate but it creates a reasonable doubt. Other people who had custody included three government doctors," he said.
Ramkarpal submitted that the prosecution's contention that Supt Jude had merely cut an envelope containing samples for relabelling was "too much a simplistic view".
"Tampering is fatal. That is why we say that the trial judge was correct when he said that he cannot be 100% certain that the samples is not compromised," he argued.
He argued that the law was strict on the integrity of samples.
"If unexplained (over the integrity of samples), it ought to be taken in favour of the respondent (Anwar)," he said.
Anwar's lead counsel Karpal Singh also hit out at lead prosecutor Tan Sri Muhammad Shafee Abdullah's remarks over Anwar's move to give a statement from the dock.
Karpal said that Shafee had defended lawyer and former deputy Speaker D.P. Vijandran for a case in Ipoh where he had given a statement from the dock.
"He (Vijandran) is obviously not a low mental capacity," he said to Shafee's remarks that such a defence was to protect a vulnerable accused who is mentally not stable.
Anwar was acquitted by the High Court on Jan 9,2012 for allegedly sodomising his former aide Mohd Saiful at Desa Damansara Condominium in Bukit Damansara on June 26, 2008.
Trial judge Justice Mohamad Zabidin Mohd Diah had ruled that the court could not be 100% certain, after going through the evidence, that the integrity of the DNA samples had not been compromised.