Rachel Nguyen

Rachel Nguyen testified as a SLED forensic-serology expert. She described her scientific education, laboratory training, competency testing, and responsibilities for screening and preparing evidence.

On direct examination, Nguyen explained her processing of ammunition, firearms, vehicles, clothing, fingernail clippings, a storage-room doorknob, and a blue raincoat. She reported mixed findings, including presumptive indications on some samples and a positive Hematrace result from a Chevy Suburban steering-wheel swab. Other identified vehicle swabs were negative for identified human blood, and all 71 tested stains on the raincoat were negative for the possible presence of blood.

Nguyen distinguished serological screening and sample preparation from DNA-profile analysis. She collected touch-DNA material and forwarded prepared samples to the DNA section, but she did not perform profile comparisons or offer conclusions identifying the source of DNA.

Cross-examination focused on the limits of her findings. Nguyen corrected the number of combined .300 Blackout cartridges from seven to six and agreed that the combined result could not be assigned to a particular cartridge. She also explained that presumptive tests neither confirmed blood nor established that a result was human, and that limited firearm-swab material was preserved for DNA analysis rather than used for Hematrace testing.