The ATF's forensic biologist Caitlin Oliver testified that calling Tyler Robinson the 'major DNA contributor' does not mean what the media said it means. It only refers to one mixed sample, not the whole gun. She confirmed that mixed samples — like a mug touched by multiple people — can make someone appear dominant in a tiny patch while the rest of the object tells a different story. She confirmed the 'DNA found on gun' headline was scientifically indefensible.