Evidence contamination didn’t affect DNA analysis – experts

Thursday, July 20, 2006
Witnesses: Dr. Francisco Supe, Chief Police Investigator,
PNP Crime Laboratory
Police Senior Insp. Edmar de la Torre, forensic DNA analyst

Two forensic DNA analysts who testified today said there might have been a contamination of the evidence submitted to them for DNA testing, but it did not affect the results of their analysis.

In separate accounts, Dr. Francisco Supe and Police Senior Inspector Edmar de la Torre confirmed the possibility of evidence contamination prior to, but not during the DNA testing.

Supe and de la Torre, both from the Philippine National Police Crime Laboratory, conducted a DNA analysis on the panties of Nicole and the condom allegedly used by Lance Corporal Daniel Smith.

Both pieces of evidence yielded positive for female DNA profile but only the panties had a male DNA profile.

In cross-examining the analysts, the defense panel described how the evidence custodian at the Subic Bay Metropolitan Authority – Intelligence and Investigation Office handled the evidence before they were submitted to the PNP crime lab.

Lawyer Francisco Rodrigo, counsel for Staff Sergeant Chad Carpentier, made the analysts agree that the following could possibly result in contamination.

a. Placing the evidence together in a brown paper bag
b. Pouring the evidence on top of a table
c. Stretching the condom using the tip of a pen/ Marking the tip of a condom
d. Putting the evidence inside a non-refrigerated drawer and keeping them there for about five days (from Nov 2 to Nov. 7)

Lawyer Jose Justiniano, counsel for Lance Cpl. Keith Silkwood, added to the list the keeping of the evidence in a non-sterilized container.

De la Torre, who has been a DNA analyst for almost six years, explained that pouring the evidence on a table or keeping them in a drawer do not necessarily lead to contamination, so long as the place is dry and cool.

He added that stretching and marking would not contaminate a condom if the one handling it wore surgical gloves.

And while they agreed on the possibilities raised by the defense, both analysts expressed belief that contamination did not occur at all.

“Had there been contamination, we would have seen a mixed DNA profile in the specimens,” Supe explained.

Aiming to establish further the mishandling of the evidence prior to DNA testing, Rodrigo asked if it was proper to use a sheet of coupon bond to wrap the condom.

Rodrigo was alluding to the testimony of an IIO investigator who said that he used a sheet of bond paper to wrap the used condom that was found dangling from the garter of Nicole’s panties.

“Coupon bond is a good container for the used condom. Our principle is to use paper and wear gloves in handling the evidence,” de la Torre said.

Earlier in his testimony, Supe also said that paper containers are used for evidence that contain dried fluids. Plastic containers, he said, are unsuitable because they moisten.

Supe also dismissed the possibility that Nicole’s pants and panties were washed and cleaned before they were turned over to investigators. Had it been the case, the DNA testing wouldn’t have yielded “good results”, he said.

Defense lawyers also grilled Supe on the reliability of the DNA testing.

Basing his questions on the PNP crime lab’s DNA analysis, Justiniano started off by asking about the amount of loci (plural for locus) that the lab used for the test.

Loci are specific target areas in the human DNA where DNA profiles are generated, Supe explained.

Supe said that out of 16 accredited loci available at the PNP crime lab, they used 12 when they conducted the test; but the standard number of locus actually needed for DNA testing is only nine.

Justiniano also questioned the lab’s use of partial DNA profiles.

Supe reasoned that they cannot choose the specimens they work on. He added that although they are a bit degraded, partial DNA profiles could still yield accurate results for DNA analysis.

Justiniano also brought up the issue of the unreliability of Florence test, which the crime lab used to detect seminal stains on the panties and the used condom.

Supe admitted that the test is inaccurate.

For the DNA analysis, however, Supe’s team used the microblue test, which is more accurate than the Florence test, to detect body fluids on the two specimens.
Asked why the PNP still uses the Florence test, Supe answered, “We are under the government. We utilize whatever is available.”

Defense lawyers also questioned the doctor on the quality of the reagents used for the DNA testing.

Supe acknowledged that the PNP crime lab uses inexpensive reagents bought from an accredited supplier known only as Sikura.

When asked by state prosecutor Hazel Valdez if using inexpensive reagents compromised the quality of their DNA analysis, Supe firmly said, “Definitely not. We stand by our results.”

He further said that “inexpensive doesn’t necessarily mean inferior quality”.

While Rodrigo and Justiniano tackled the technical aspects of the DNA analysis, counsels Benjamin Formoso for Smith and Enrico Uyehara for Lance Cpl. Dominic Duplantis dwelled on its findings.

Formoso and Uyehara concentrated their questioning on why only the panties had a male DNA profile and the condom had a female DNA profile inside it.

Formoso asked if it was possible for a man’s DNA to be transmitted to a woman’s panties during intercourse.

With his forehead creased, Supe said: “I can’t relate to your question, sir. You remove the panties when you engage in sex.”

Formoso reformed his question and added transmission through saliva.

The doctor said that it was possible only if “the man was kissing the panty.”

Some of the court audience, and even the lawyers and presiding Judge Benjamin Pozon laughed at the exchange.

Formoso then asked: “If a man and a woman are sweating heavily because of dancing, is it possible that the man’s sweat would be transferred to the woman’s underwear?”

Supe said it could happen only if they danced very close to each other.

Uyehara also inquired if it was possible for a woman with sweaty hands to get her DNA profile on a condom if she assisted the man in putting it on.

Supe answered in the affirmative but clarified that the DNA would have to be outside the rubber.

Explaining why there was no male DNA profile in the condom, Supe said it could be because the genetic material degraded due to heat, moisture, enzymes and other factors.

During redirect examination, Valdez made Supe admit that he received a letter from Formoso, dated June 14, 2006, requesting for a copy of the results of the DNA testing.

The doctor said that since he was undergoing schooling that time, he rerouted the letter to his superiors and waited for their instructions.

Earlier on cross-examination, Rodrigo asked Supe if any of the prosecution lawyers contacted or approached him to discuss the results of the analysis.

Supe said no one did and added that he didn’t give out any copy of the result until the court sent a subpoena for it.

Meanwhile, under the questioning of state prosecutor Elizabeth Berdal, de la Torre narrated to the court what the specimens, the condom and the panties, went through in the process of DNA testing.

De la Torre said the specimens were first screened, but he wasn’t there when it took place.

He further said that DNA materials were extracted from the specimens, then “photocopied” using polymerase chain reaction (PCR), and analyzed.

In his analysis, de la Torre indicated that the female DNA profile found in both the panties and the condom matched that of Nicole.

Nicole had given the crime lab her blood sample to be used as reference and control sample for DNA matching.

De la Torre also backed Supe’s testimony that no contamination of evidence occurred.

“If there was contamination and the contaminant was another human DNA profile, it would have been reflected in our analysis,” he said.

He added that if the contaminant was other than DNA, it would not really affect the results of the test because the “components in the machine used for DNA testing are specific only to DNA.”

Asked if it is easier to contaminate a PCR than to catch a common cold, de la Torre said no. He, however, agreed that DNA matches are not the end of the inquiry but only the beginning of investigative work.


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