Click on "Who's This Pumpkin Head Anyway?" after the game starts and you get to it. Click "Who Was The Hostage?". Obviously, click "Are There Any Suspects?". Go to the mayor's office. Click on the office to go inside it. Go up to the secretary and click "That's all thank you".
Click the door to go outside. Go to the desk to get the letter. Give the letter to the secretary. Go to the police station. Click "Consult Notes And Ask About Evidence".