Question: After Harry discovers that Peter is really Spider-Man, he tells Peter that he murdered Norman Osborne. Why didn't Peter just say, "I didn't kill your dad. He was already dead when I brought him to you"?
Answer: As the other answer suggests, it'd be a dangerous waste of time. Additionally, Harry is literally driving himself insane believing that Spider-Man killed his father... so it's not like Harry would actually believe Peter anyway even if he tried to explain it in that moment.
But, surely before he left, he would have had just enough time to quickly say, "I didn't kill your dad. The Green Goblin did."
That's not the point. The point is, Harry wouldn't have believed him... he's too far lost in grief and revenge. This is further evidenced when Peter tells him in "Spider-Man 3," and Harry refuses to believe him.






Answer: Anything Peter tells Harry about his dad at this point could lead to Harry asking more questions, and Peter wants to get to Doc Ock's lab before it's too late.
Phaneron ★