Includes guest stars Justin Bruening (Rob Tredwyck), Brendan Hines (Alex Conrad), and Erik Palladino . Official Summary: View more on Apple TV or Rotten Tomatoes .

A former Olympic champion and Zack's mentor. It is revealed Rob was a long-term steroid user; he killed Zack to prevent his secret from being exposed.

Zack was drugged with powdered chlorine and drowned in the UNY training pool. Key Suspects & Motives:

Zack's best friend; the two had been stealing cars together to help Zack afford basic necessities while training. Subplots & Themes

In the Castle episode (Season 3, Episode 21), Castle and Beckett investigate the murder of Zack Lindsey , a promising Olympic hopeful found dead in his college training pool . The investigation reveals a dark underworld of steroid use and car theft . Case Breakdown

A rival swimmer who used undetected steroids supplied by the coach.

Castle seeks counsel from real-world authors Michael Connelly and Dennis Lehane during their recurring poker game, though they are notably aloof toward his new protégé. Episode Details Original Air Date: April 11, 2011.