On June 27, 1995, LAPD criminalist Susan Brockbank took the stand in a Los Angeles courtroom and began explaining to the jury of the People v. Orenthal James Simpson something they had likely never encountered: what textile fibers look like under a microscope, and why they mattered in a double murder case. Her testimony that morning opened the prosecution's fiber evidence chapter — a methodical effort to stitch a physical connection between Simpson's White Ford Bronco and the Bundy Drive crime scene where Nicole Brown Simpson and Ronald Goldman had been stabbed to death the previous summer.
Brockbank was a qualified expert in microscopic hair and fiber analysis with the Los Angeles Police Department. Fiber comparison works by measuring characteristics that can be seen under magnification — color, diameter, cross-sectional shape, surface texture — and comparing them against known reference samples. When two specimens share a sufficient cluster of characteristics, an examiner can testify that they are consistent with a common origin. What the science cannot say, and what Brockbank could not say, is that any two samples definitively came from the same garment. It is a discipline of consistency, not identity.
The prosecution had built its fiber case around a specific physical connection. A black knit cap had been found near Ronald Goldman's body at the crime scene on Bundy Drive. According to evidence presented at trial, fibers from the carpeting inside Simpson's Bronco closely resembled fibers found on that cap — a match that, if accepted by the jury, placed Simpson's vehicle in the same physical universe as the scene of the killings. A second fiber connection linked the Bronco's interior to a bloodstained leather glove discovered at Simpson's Rockingham estate. The blood on that glove matched DNA profiles from both victims.