Expert witnesses often give key testimonies at criminal trials and are allowed to give their own opinions. But what happens when their opinions don't reflect the facts?  "48 Hours" correspondent Susan Spencer, Harold Dow and Peter Van Sant report. This classic "48 Hours" episode last aired on 8/23/1999. Watch all-new episodes of “48 Hours” on Saturdays and stream on demand on Paramount+.

Inside D4vd's Preliminary Hearing in Murder Case

“48 Hours” uncovers the narrative behind crime and justice cases that have left a lasting mark on society. Award-winning CBS News correspondents thoughtfully examine the complexities of each crime by transporting you to the heart of the investigation through key evidence and gripping interviews with critical figures from the case. The unmatched reporting has made a tangible difference in countless lives, leading to the exoneration of wrongly convicted individuals and the reopening — and resolution — of previously closed cold cases.Listen to a new “48 Hours” episode every Monday&nbsp;and&nbsp;then go deeper into the case on Tuesdays with the immersive “Post Mortem” series — producers and correspondents join host Anne-Marie Green to discuss key evidence, dead ends, mishaps, and stranger-than-fiction twists they faced in the field. Also available on the 48 Hours YouTube channel. Plus, every Wednesday and Thursday, we’ll revisit a classic “48 Hours” episode.&nbsp;Get ad-free access to 48 Hours podcasts by subscribing to 48 Hours+. Subscribe at 48HoursPodcasts.com, then listen in Apple Podcasts, Spotify, or use your private link in your favorite podcast app.