Three witnesses testified to the scientific validity of tool mark examination Wednesday in a hearing for James Genrich, who was convicted of setting a series of pipe bombs in Grand Junction in 1991 and is seeking a new trial.

Colorado Bureau of Investigation Firearm and Tool Mark Examiner Julie Knapp said Wednesday that tool mark examination is a recognized forensic science and has been for more than 100 years.

Tool mark examination was a key component Genrich’s conviction, but its scientific validity has been called into question in recent years.

At the time, examiners said they had matched two pairs of pliers and a wire stripper owned by Genrich to wires on a pipe bomb that had not exploded in 1989 (Genrich was living in Phoenix at the time, but prosecutors argued he had used an unnamed accomplice).

Knapp also defended the quality assurance, ethics and professional standards of the Association of Firearm and Tool Mark Examiners (AFTE), the practice’s professional organization.

Knapp, who said that she is not a certified tool mark examiner because she hasn’t had the time or resources to take the certification test, was tasked in 2014 with reviewing findings by CBI examiner Dale Higashi, who himself was tasked with testing the original findings.

During her verification, Knapp said, which was independent of Higashi’s, she used Higashi’s microscope in Denver and did not take intensive notes on the process she used at the time.

Knapp said she wasn’t aware of the case before or during the verification, and didn’t even know about the bombings even though she grew up in Grand Junction.

Knapp testified that tool examination relies on chip formation, which occurs at a microscopic level during manufacturing and creates “unique, random” chips investigators can look at.

The markings left behind by tools can create unique patterns, Knapp said, which can be matched.

However, Knapp said, this generally doesn’t involve measuring the depth, width or height or markings.

Instead, Knapp said, the investigators are trained to recognize patterns and the thresholds for identifying a match are subjective and often based on memory.

According to Knapp, the threshold for an identification is”when you have sufficient agreement in the form of a pattern.”

“I do have a memory and it was updated with other images from the internet,” Higashi said regarding tool mark examination.

Knapp noted things like angle and pressure can change the marks a hand tool makes, and she said every tool mark is unique, but there are sub classes examiners can look at.

Higashi and Knapp both said they were not aware of any errors discovered in their casework over the course of their respective careers.

Firearm and tool mark consultant Ronald Nichols also testified Wednesday, saying there have been machine-based studies that validate tool mark examination as a discipline.

The hearing is scheduled to continue at 9 a.m. Monday.