Justice Breyer noted the pervasive use of expert witnesses in modern litigation:
"Scientific issues permeate the law. Criminal courts consider the scientific validity of . . . DNA sampling or voiceprints, or expert predictions of defendants' 'future dangerousness,' which can lead courts or juries to authorize or withhold the punishment of death."
Some legal scholars, editorialists, and others argued that juries must be protected from the scourge of junk science.
Like-minded judges began to scrutinize scientific evidence closely before admitting it at trial and to exclude evidence that did not meet their strict standards.
Other judges were content to rely on the adversarial system to reveal any flaws in tendered scientific evidence. These judges favored admitting any scientific evidence that seemed relevant, and therefore rarely excluded scientific evidence before trial.
The advent of DNA evidence, dramatically changed the legal landscape.
The initial DNA skirmishes over laboratory protocols quickly morphed into fights over statistical interpretation and population genetics.
The initial technique, Restriction Fragment Length Polymorphism (RFLP), was soon supplanted by Polymerase Chain Reaction (PCR) involving the DQ-alpha loci, which was followed by Polymarkers (PM) and D1S80.
These, in turn, were replaced by Short Tandem Repeats (STR), the current procedure.
In addition to nuclear DNA, mitochondrial DNA analysis and animal and plant DNA evidence have been introduced in criminal cases, raising further evidentiary questions.
Finally, the use of DNA databases for "cold hits" has presented its own fundamental issue: whether DNA evidence alone is sufficient to uphold a conviction.
The Department of Justice's 1997 report on the FBI laboratory, issued by the Inspector General, graphically described negligence, misconduct, and other shortcomings of the premier crime laboratory in the country.
The investigation found scientifically flawed testimony, inaccurate testimony, testimony beyond the competence of examiners, improperly prepared laboratory reports, insufficient documentation of test results, inadequate record management and retention, and failures of management "to resolve serious and credible allegations of incompetence."
Prosecutors (and other government lawyers-lawyers in enforcement agencies, who use scientific evidence) want a liberal standard of admissibility, or at least a standard that will apply in the same way to both the prosecution and the defense
IN HIS BOOK LABORATORY OF JUSTICE, David Faigman takes the Supreme Court to task for persistently failing to inquire into the merits of the scientific evidence figuring in the cases before it.
"For 200-plus years the Court has demonstrated remarkable insensitivity to empirical questions," he contends. "Its factual jurisprudence is slapdash, sloppy, and, too often, supercilious."
Was this a proper exercise of (Daubert) gatekeeping power?
The dissent questioned whether it was not more sensible to admit testimony based on accepted scientific principles of engineering, and let the jury consider the points made by defendant as matters going to the weight and not the admissibility of the evidence
expert witnesses can be "co-opted" by the prosecution-they may be little more than hired guns of the state.
Even honest witnesses who are trying to be objective may not be asked the right questions and may have their testimony filtered or contorted by the advocate.
"Untoward results follow when expert evidence in complex cases is presented in adversarial fashion: Expert witnesses are manipulated for partisan purposes, some relevant scientific findings are never introduced, and unwarranted conclusions are not distinguished from valid research “ . . .
Forensic scientist D.H. Garrison, Jr. puts it this way:
"Bad science is what forensic science becomes when an attorney or prosecutor, who often display(s) all the ethics of a full-grown hamster, get(s) a forensic scientist to play ball, to get with (the advocate's) program and see (the advocate's) big picture."
Sometimes prosecutors will "shop around" until they find an expert who will tell them what they want to hear.
This happened in the infamous Rolando Cruz case. ]
The first lab guy says it's not the boot. . . . We don't like that answer, so there's no paper (report). We go to a second guy who used to do our lab. He says yes. So we write a report on Mr. Yes. Then Louise Robbins arrives. This is the boot, she says. That'll be $10,000. So now we have evidence
. . . a court order to re-score the autorads with the computer imaging device watched by counsel and an independent expert
In order to detect bands in the male vaginal extract lane that corresponded to those of suspect 1, the analyst had to increase the sensitivity of the computer to the point that it detected many additional "bands" that matched neither suspect.
The analyst then performed a "manual override" of the computer's scoring, instructing the computer to "delete" (i.e., ignore) all of the bands that matched neither suspect.
The analyst’s explanation?
He could tell by looking that the undeleted bands, were "true" bands while the others were not.
In fact, a number of the deleted bands he deleted had higher optical densities than the bands scored as matching suspect # 1
"'(c)onsistent with' is one of those catch-all phrases that means (little more than) something could be possible. It is used a lot . . . especially on the witness stand when evidence can be interpreted in more than one way."
Later Captain Proctor would give an affidavit that he was never able to find any convincing evidence to support another expert's testimony that the bullet was marked with scratches to prove it went through Sacco's pistol.
He also said he told the district attorney he would answer "no" if he were asked if he had found any such "affirmative" evidence, but that he had not been asked that question at the trial.