why does the the burning of Anja's diaries upset Art?

Art asks his father again about Anja's diaries, and Vladek says that they can't be found, because he burned them after Anja died. Vladek was depressed, and there were too many memories in those pages. All Vladek can remember about the content of the diaries is a sentence wishing that her son would one day be interested in them. Art is furious and screams at his father, calling him a murderer. This is from the gradesaver site. Check out the source link below!