On the Rankin-Selberg integral of Kohnen and Skoruppa

The Rankin-Selberg integral of Kohnen and Skoruppa produces the Spin L-function for holomorphic Siegel modular forms of genus two. In this paper, we reinterpret and extend their integral to apply to arbitrary cuspidal automorphic representations of PGSp(4). We show that the integral is related to a non-unique model and analyze it using the approach of Piatetski-Shapiro and Rallis.