Janet Walsh was murdered by strangulation in her apartment. The police questioned Gregory Hopkins, who admitted that he had a casual sexual relationship with Walsh during the summer but denied being present when she died. Having no evidence to the contrary, the investigation languished.
Walsh died in 1979. More than three decades later, advances in technology allowed Pennsylvania to test crime scene evidence for traces of DNA. The police reopened the investigation and discovered the presence of Hopkins’ semen on items that were on or near Walsh’s body.
Since Walsh admitted having a sexual relationship with Hopkins, the presence of his semen was consistent with his innocence. Having no evidence that the semen was deposited at the time of Walsh’s death, prosecutors strengthened their case by calling a forensic pathologist, Dr. Cyril Wecht, as an expert witness.
Dr. Wecht opined that “topographical distribution” of Hopkins’ semen proved that he was present at the time of Walsh’s death. The jury accepted that testimony and found Hopkins guilty of third-degree murder.
After Hopkins’ conviction was affirmed on appeal, Hopkins filed a postconviction motion based on his trial lawyer’s failure to seek exclusion of Dr. Wecht’s testimony. On appeal from a denial of that motion, the Pennsylvania Superior Court agreed that Dr. Wecht should not have been allowed to present his novel “topographical distribution” theory as an expert opinion.
Walsh separated from her husband shortly before her death. When her body was discovered, her hands were bound behind her back with the belt from her bathrobe. Walsh was wearing a nightgown and her body was covered by a sheet. A bandana around her neck had been used to strangle her.
The sheet had been placed on Walsh’s body by her father when he discovered her body. The sheet was removed and replaced multiple times by police officers, including the investigating trooper. The trooper examined the scene closely but saw no wet spots or stains on the sheet or on Walsh’s nightgown. Forensic specialists took swabs from Walsh’s mouth and vagina but found no evidence that Walsh had engaged in sexual activity at the time of her death.
The best suspect appeared to be a drifter who danced with Walsh at a club and then went to a restaurant with her in the late-night hours before her death. The drifter’s checkbook was found in a gutter near Walsh’s apartment.
Hopkins candidly admitted to the police that he had sex with Walsh several times during the summer. Their last sexual encounter was about three weeks before her death. He denied being with her (and nobody claimed to have seen them together) on the evening before her death.
When the investigation reopened in 2010, forensic investigators used a technique to identify traces of semen that are invisible to the naked eye. Forensic investigators testified that they found semen on the sheet, the bathrobe belt, and the nightgown. Although much of the semen had degraded and could not be reliably tested for DNA, investigators testified that DNA found in some samples came from Walsh. No DNA was found on the bandana that was used as a murder weapon.
The forensic investigators admitted that they did not know when the sheet, nightgown or bathrobe belt had last been washed. They also admitted that no test can identify the date on which semen is deposited prior to its collection for testing.
The prosecution nevertheless constructed a theory that Walsh died during a sexual encounter with Hopkins. That theory was unsupported by any physical evidence and was inconsistent with evidence that no semen was found in Walsh’s vagina. In addition, a physical examination of Walsh’ body in 1979 revealed no evidence of recent sexual activity.
Undeterred by the absence of any evidence that Walsh had sex on the night of her death, the prosecution obtained an expert report from Dr. Wecht to bolster its case. Dr. Wecht is an experienced forensic pathologist. He concluded that Hopkins’ semen had been deposited on the night of Walsh’s death.
Dr. Wecht based his opinion on the placement of the semen on Walsh’s bathrobe belt, nightgown, and bed sheet. He concluded that the location of the semen somehow established that Hopkins was on the bed on top of Walsh’s back at the time of her death. Dr. Wecht’s “topographical distribution” theory suggested that Hopkins strangled Walsh while he was having intercourse with her from behind.
Dr. Wecht admitted that DNA can be transferred from one object or location to another when objects are handled or laundered, although he discounted that possibility in this case. He could not explain why trained investigators failed to observe fresh semen stains if they had been deposited just hours before Walsh’s body was discovered.
Two defense experts (a forensic pathologist and a DNA expert) challenged Dr. Wecht’s opinions. They agreed that the semen could have been deposited prior to the night of Walsh’s murder.
Challenge to Dr. Wecht’s Testimony
Hopkins’ counsel challenged the admissibility of the opinions provided by Dr. Wecht on the ground that they were not stated to a reasonable degree of medical certainty and that they were not scientific opinions and thus not helpful to the jury. Counsel did not challenge the opinions on the ground that they failed the Frye test.
The trial judge agreed that Dr. Wecht identified no scientific principle that allowed him to determine from semen “placement” the date on which the semen was “placed.” The prosecution appealed that pretrial ruling. In a cursory 2-1 opinion, the Superior Court concluded that the testimony was admissible under Pennsylvania’s liberal standard for the admissibility of expert evidence. The dissenting judge agreed that Dr. Wecht’s opinion was unsubstantiated by any scientific principle and was therefore an inadmissible lay opinion rather than expert testimony.
Pennsylvania has consistently rejected the Daubert standard of admissibility. It has adhered to the Frye standard for decades and incorporated Frye’s “general acceptance” standard into the state evidence code shortly before Hopkins’ trial.
The appellate court emphasized that trial counsel’s challenges to Dr. Wecht’s testimony did not specifically include a Frye challenge. That is, he did not argue that testimony based on a “topographical distribution” theory was inadmissible because the theory was not generally accepted by the scientific community.
At a hearing on his post-conviction motion, Hopkins presented the expert testimony of two forensic pathologists: Dr. David Fowler, the chairperson and former president of the National Association of Medical Examiners, and Dr. Kimberly Collins, the incoming president of that association.
Both experts testified that Dr. Wecht’s topographical distribution theory is “not medical science” and that engaging in a topographical distribution analysis is outside the boundaries of accepted practice in the field of pathology. In fact, neither expert had ever heard of the theory before.
While Pennsylvania courts recognize the admissibility of expert testimony based on novel theories, those theories must be founded on methodologies that are generally accepted by the scientific community. General acceptance can be established from a variety of sources, but an expert’s personal opinion is not enough. The opinion must be supported by recognized scientific authority.
In deciding the post-conviction motion, the trial court recognized that Dr. Wecht’s topographical distribution theory had no scientific validity but bizarrely concluded that his testimony was admissible precisely because it was not based on science and was therefore not subject to the rules governing the admissibility of expert opinions.
The appellate court recognized that the trial court’s decision would make all expert testimony admissible, whether or not it was based on generally accepted principles of science. The prosecution presented Dr. Wecht as an expert and urged the jury to accept his expert opinion. An opinion that purports to be based on science must be supported by a generally accepted methodology.
The prosecution argued that Dr. Wecht’s conjecture was supported by “common sense.” However, common sense is not science. Juries and lay witnesses are entitled to use their common sense. Experts in science must be guided by science.
Since Dr. Wecht’s opinion was supported by nothing beyond his own conjecture, his opinion was inadmissible. The appellate court concluded that Hopkins’ counsel was ineffective in failing to seek exclusion of the testimony on Frye grounds. Had he done so, the testimony would have been excluded. And without Dr. Wecht’s testimony, no evidence supported the theory that Hopkins was present at the time of Walsh’s murder. Hopkins is therefore entitled to a new trial.