Why do I need a subpoena to get a copy of a statement another individual made in a police report?

An altercation happened to me. I have received a copy of the police report and a copy of the statement I wrote out to the deputy who was called out to the scene of the altercation. I tried to get a copy of the statement the other individual wrote out to the deputy but was told by the deputy I need to get a subpoena from a judge to get the other individuals statement. Is this true? If so, why?