Derek Yoo

 is one of Jacob Barber's closest friends. He attends Archer Middle School with Jacob, Sarah Grohl, and the late Benjamin Rifkin.

After Ben's body is discovered, Derek implicates Jacob in the murder by accusing him of committing the crime and pointing out he had a knife. This, along with a fingerprint found on Ben's body, leads to Jacob's arrest.

Suspicions are raised about Derek when Sarah reveals to Andy Barber that Derek had Ben's mobile phone. Sarah recounts to Andy that Derek wanted a relationship with her but instead she was getting on with Ben. After Ben wanted her to send revealing images, Derek found out about this and took Ben's phone off him two days before the murder. Sarah refused the phone once Derek had tried to give it to her, which led to the pair falling out.

Sarah is tipped off Pam Duffy that Derek had motive for the murder and the police indeed brought in Derek and Dina Yoo for questioning. Andy also questions Derek off the record, for which Derek denies any involvement in the murder and suggests Jacob is not to Andy thinks he is.