20/20 - Season 2026 Episode 1 -

Dan Markel was a prominent Florida State University law professor. But in 2014, he was found gunned down in his Tallahassee home. As authorities begin investigating his murder, they identify someone close to home as the possible mastermind behind the killing: Donna Adelson, Dan's former mother-in-law. Dan was embroiled in a bitter divorce and custody battle with Donna's daughter, Wendi, and prosecutors say this 75-year-old grandmother orchestrated an elaborate murder scheme. "20/20" has followed this case for more than a decade. Correspondent Ryan Smith brings viewers inside the twists and turns of this case, including the latest on the trial, verdict and murder that shattered a family and shocked the nation.