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The Scientific Method Expert | State v. Romero

Case Analysis:

State v. Romero (2016)

The Arizona Supreme Court Rules that the Scientific Method is a Proper Subject for Expert Testimony and Cross-Examination

Scientific Method Experts and Daubert
Relevant Facts
Trial Court
Opinion at Issue
Court of Appeals
Supreme Court

Basic Facts

Victim is Shot

The victim was killed by two gunshot wounds. Six shell casings were found at the scene.

The Police Find...

Police later discovered a gun along a path Romero had just traveled.

State v. Romero (Facts)
A Police Ballistics Expert

Years later, a government firearms expert conducted ballistics tests on the gun found near Romero. Based upon his testing, the expert concluded the indentations the gun left on the shell casings matched those on the shell casings found near the body.

State v. Romero (Powell Opinion)
Romero is Charged

The State charged Romero with murder based upon their expert's opinions.

Procedural History

First Jury Trial. The government’s firearm expert testified and concluded the casings at the scene matched the gun found near Romero.  However, a mistrial resulted.


The scientific method is a fundamental process. It uses logical steps to answer questions. It is only by properly following every step, that is required in a specific circumstance, can you determine if something is the product science or not?

Skip a necessary step – and your results – cannot be relied on.

Failure to properly conduct a necessary step – and your results – cannot be relied on.

Subsequent Rule 702 Hearing. After the mistrial but prior to the second trial, Romero moved to exclude the government expert testimony. The trial court held a Rule 702 hearing applying the principles set forth in Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993). 

At the hearing, Romero presented the testimony of an expert in the requirements of fundamental scientific methods.  Romero’s expert, Dr. Haber, at the hearing:

  • Stated the general features of conventional toolmark comparison testing that fell short of scientific standards for experimental design.
  • He further testified that those failings limited the scientific weight that could be placed on the results of any such test.
  • Opined that the tests, even if conducted correctly, could not scientifically justify the conclusions that the government sought to draw.
State v. Romero (Court of Appeals Ruling)

Dr. Haber was not offered to:

  •  Comment on the facts of the case
  • To opine whether Powell was “right or wrong.”

The trial denied Romero’s motion to preclude the government’s expert’s testimony.  However, the court went a step further.  At the same it granted the government’s motion to preclude Dr. Haber from testifying as a defense expert at the jury trial.

The Second Trial. Romero was acquitted of first-degree murder.  However, he was convicted of second-degree murder.  

Arizona Court of Appeals

Arizona Court of Appeals.  The Court of Appeals affirmed the conviction. See State v. Romero, 236 Ariz. 451, ¶¶ 18-32 457-60 (App. 2014)). A majority of the court of appeals’ panel affirmed the conviction and the exclusion of Romero’s expert’s testimony.

Arizona Supreme Court

The Scope of Review

The court agreed to review only the trial court court’s ruling regarding the preclusion of Dr. Haber’s testimony at trial.  The Court did not review the denial of Romero’s Daubert challenge regarding the government’s expert. 

State v. Romero (Supreme Court Issue)

The Issue

The Court frames the issue as whether Romero’s expert was qualified in field that he was offer for at trial – experimental deign.

State v. Romero (Expert Design)

The Purpose Dr. Haber's Testimony

Dr. Haber’s testimony served more than one purpose.  While the trial did not find it persuasive enough to grant Romero’s Rule 702 Motion – Romero also sought to use it to persuade the jury.

State v. Romero (Purpose of Haber)

The Court correctly stated why Romero was calling Dr. Haber at his jury trial: “the methods generally used in conventional toolmark analysis fall short of scientific standards for experimental design.”

The purpose of Dr. Haber’s testimony went to “the scientific weight” the jury should (or should not) give the government’s expert testimony.  

Qualified for His Purpose

Dr. Haber was an expert in the field of experimental design.  Put another way, he was an expert regarding the fundamental requirements of the scientific method.

The Arizona Supreme Court found: “[w]ith respect to experimental design, and a comparison of the methods generally used by firearms examiners to the scientific method, Dr. Haber is qualified as an expert.”

Helpful to the Jury

Rule 702 requires that expert testimony be “helpful” to the jury in understanding the evidence. Ariz. R. Evid. 702(a).

The purpose of the government’s expert’s testimony was to match the shell casings to the gun. The bases of this conclusion were “toolmark comparisons.” The government’s expert quantified his match opinion was to “a reasonable degree of scientific certainty.

Accordingly, the Supreme Court found “Dr. Haber’s testimony would have been helpful to the jury in understanding how the toolmark analysis differed from general scientific methods and in evaluating the accuracy of Powell’s conclusions regarding ‘scientific certainty.’”

The court also explained how the testimony could be helpful:

Subjective Determinations

Dr. Haber’s testimony was that the methods underlying toolmark analysis “are not based on the scientific method.” Rather, they are merely the “subjective determinations” by the examiner conducting the analysis.

Weight of the “Scientific” Conclusion

Firearms examiners don’t follow an accepted method for evaluating characteristics of fired shell casings and comparing them to control subjects. Dr. Haber could have helped the jury assess how much weight to place on Powell’s “scientific” conclusion that the shell casings at the murder scene could only have been fired from the Gun found by the police near Romero.

 Educating about general principles.

Dr. Haber’s testimony would have been helpful despite the fact he did not perform a toolmark analysis.

Not a Second Daubert Hearing

The Supreme Court determined that the “trial court’s alternative ground for preclusion was an error of law.”

  • The trial court’s reasoning “fail[ed] to recognize that very often the same proof used to establish admissibility also impacts weight and credibility.” 
  • Blanket preclusion at trial of evidence presented at a pretrial hearing “infringe[s] upon the role of the jury and improperly insulate[s] the state’s evidence from critique.” 

The trial court’s alternative ground for preclusion was determined to be an error of law.

In the End...

The Supreme Court “vacate paragraphs 19 through 32 of the opinion of the court of appeals.”  It also remanded the case to the court to determine if the exclusion Dr. Haber’s testimony was “harmless.”

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