Meursault tells the reader his mother died in the first line of the novel. She was living at The Home for Aged Persons in Marengo near Algiers and the reason there weren't many people at her funeral is that, as they state on page 18, "it was a rule of the home that inmates shouldn't attend funerals." In the end, aside from his mother's nurse, only Meursault and his mother's "special friend" M. Perez attend.
The funeral and Meursault's reaction to it becomes an essential part of the prosecution's case to convict him as a coldhearted killer. The police claim that he showed "great callousness" at the funeral, the undertaker says he didn't know his mother's age, and a warden says he left as soon as the funeral ended. After it is proved he didn't shed a tear over his mother's death, his girlfriend Celeste tells the court that she started her relationship with Mersault the day after the funeral. To the court, it proves the Meursault is capable of murder.
Meursault finds it disappointing that his lawyer does not bring up the funeral in his final address to the court. At that point, however, he is so numb that as he states "everything was dissolving into a grayish watery haze."
The novel ends with Meursault in prison waiting to be executed.