A DNA sample extracted from a person can be conserved for years under the right conditions, said a forensic expert today.

The expert, who declined to be named, cited the 1994 sex scandal involving former US president Bill Clinton.

"(Monica) Lewinsky kept her dress in the cupboard for two years and the DNA was preserved.

dna testing 180708 "Saliva, blood and seminal stains when stored in proper conditions can be preserved - by not exposing the sample to rain, sunlight and other natural elements," he told Malaysiakini .

"It could be kept at room temperature like in a cupboard," he added.

Asked if any foreign DNA in a person’s body can be detected after several days, the expert said it would depend on the location of the stains.

"When rape had taken place, there will be seminal stains in the private parts, the underwear and such. But if the victim washes himself or herself, then you wash the DNA sample away as well," he said.

'Cannot be manipulated'

The expert said while a DNA sample cannot be manipulated, it can however be planted as evidence.

"If it (the DNA) is there, it's there, if it's not there, it's not there. But manipulation of evidence may occur if (say) you go to the blood bank, get a pint of blood and plant it on the mattress," he said.

The expert stressed that DNA evidence alone is not sufficient to proof a case.

It usually function as a "collaborative evidence" in the investigation of a crime but other evidence will still be required.

"CCTV footage and other evidence are needed," he said.

He also stressed that the forensic department is only limited to analysing the sample, and not determining how the sample was found.

anwar ibrahim 1998 sodomy trial court case the bed mattress stain tilam dna 180708 "The analysis in the forensics department is limited to only finding out if there is any sample on a mattress (for example).

"It is not their job to infer how that sample got on the mattress. That's the police’s duty.

"Forensics' duty is only to analyse and conclude that there is blood on the mattress but they can’t infer how the blood arrived on the mattress," he said.

Anwar's case

Elaborating on the importance of a blood sample, he said it is needed to confirm the actual owner of, for example, a semen stain.

"When we analysed a DNA sample like hair strand or semen discharge, we only learn if it is a male or female profile.

anwar out from hospital 160708 01 "Hence, we need the blood sample to have a comparison specimen (to match the owner of the DNA sample)," he said.

DNA has become a key issue since the July 16 arrest of PKR de facto leader Anwar Ibrahim, who is facing fresh sodomy allegations.

The politician - who claims this is a conspiracy - has refused to provide the police with his DNA sample for fear that it could be manipulated.

The police are now considering seeking a court order to compel the opposition leader to provide a DNA sample.

There was an unsuccessful attempt to use DNA evidence in the prosecution of Anwar in 1998 for similar sodomy charges.

Prime Minister Abdullah Ahmad Badawi today said that the authorities require a fresh DNA sample from Anwar because the existing sample is too old.