It’s very similar to the plot of John Q with Denzel Washington. This is the plot summary from https://lawandorder.fandom.com/wiki/Undercovered

Warren Slater, an executive at The Fairhaven Group, an insurance company, is found dead by a street sweeper on Riverside Drive. Briscoe and Green are led to Tony Garcia, a policy holder at Fairhaven, and Slater was supervising his policy. The policy in question is for Garcia’s 9-year-old daughter, Courtney, who has leukemia.

Garcia was upset that Fairhaven was denying Courtney the only treatment that he felt would save her life -- an experimental drug called Gleevec -- because Fairhaven saw it as too expensive ($2,500 a month for the rest of her life). Garcia killed Slater because he felt that it was the only way to save Courtney’s life, since Slater was practically killing her by denying her the treatment she needed, and backed a cheaper bone marrow transplant plan that wouldn't have worked out, instead.

McCoy prosecutes the case, but after Garcia testifies, the jury is deadlocked, and the Judge has no choice but to declare a mistrial. Lewin decides that no jury would unanimously vote to convict him, and so it's not the kind of case that they want to try again, so Garcia is a free man.