A party gone wrong

One dark and stormy night, Prof. David hosts a party at his mansion. He invites a whopping 1,000 people over. Only 20 minutes into the party, all of the lights flickered off.the was a sudden blood curdelling scream. The lights flickered back on and the Professor was dead! His body was covered in scratches and there was a knife stabbed into his back. Everyone gathered around his body. All except you. You were standing around by the painting wall, looking at an amazing artwork of a detective daydreaming about what it would be like to be one. As you got brought back into reality, a stranger ran past you wearing a black coat and cape and holding a knife. What Will you do next?