Fallet G (2006)

A woman suspects that her husband is having an affair and hires a hard-drinking private detective to spy on him and find out whether that is the case. When the woman is later found dead at the bottom of a drained swimming pool, investigators believe it was an accident. Van Veeteren, however, discovers that the husband is an old acquaintance and archenemy, Jaan G. Hennan (also known simply as G), and becomes convinced that it was murder. The major problem for Van Veeteren is that Hennan has an airtight alibi, meaning the prosecutor cannot bring him to justice. Seven years later, private detective Maarten Verlangen mysteriously disappears, prompting Van Veeteren to reopen the old case, determined to solve the murder and bring his old archenemy to trial. The film/book’s title, The G Case, comes from the fact that the suspect was known simply as “G.”