Final answer:
Derek has committed the offence of an Accessory after the fact by helping Jordan, who has committed a serious criminal offence, to conceal the crime afterwards.
Step-by-step explanation:
If Jordan commits a serious criminal offence and Derek then helps Jordan conceal this offence, Derek has committed the offence known as an Accessory after the fact. This legal term refers to someone who, knowing that a crime has been committed, acts to obstruct justice by helping the perpetrator evade law enforcement or prosecution. Derek did not commit the initial offence, nor was he involved before or during the commission of the crime, but by helping to conceal the crime afterwards, he becomes an accessory after the fact.