A young adult novel with an early-teen female protagonist. Some sort of a murder, perhaps an elderly neighbor. I vaguely recall a police sketch of the killer (a man with glasses). The killer turns out to be a member of the family (or close acquaintance), and I vaguely recall lots of people milling around during the final scene while the young girl frantically tries to identify the killer from amongst the guests (like lots of people visiting for a festivity, possibly even the wake). She finally identifies him and ends up scaling a crab in the apple  tree to get away before he is finally stopped. It’s possible she witnessed the murder from this same tree.