Did depends on the wording like me I us we or he, him, his, himself, she, her, hers, herself, it, its, itself, they, them, their, theirs, and themselves. If you see I in the book you know its a first person but if uses words like they then its third person
Hey we just read that too! How Mr. Frank says "no more" because he can't bare to remember his horrid past by reading his diary. In the first scene, he finds the diary and starts reading it. In scene 5, Mr. Frank finishes the book.