Mystery nš1 Anwser
Detective Adam knew it was Emma because she took off her gorilla glove. There were no fingerprints on the knife, so the murderer had to be wearing a glove. Emma appeared to be the only one with a glove on. Also, he knew her story about how they were in the basement the day before was fake because he heard Emily talking about how Emma and her had been up north. Emma admitted to doing it because Natalie was her only competition from being valedictorian, the thing Emma wanted most in her life. She had been so desperate, she figured murder was the answer.