GA Q6

The police arrested four criminals – $P, Q, R$ and $S.$ The criminals knew each other. They made the following statements: $P$ says “Q committed the crime.” $Q$ says “S committed the crime.” $R$ says “ I did not do it.” $S$ says “What Q said about me is false”. Assume only one of the arrested four committed the crime and only one of the statements made above is true. Who committed the crime?