On Fourier coefficients of Siegel modular forms of degree two with   respect to congruence subgroups
  We prove a formula of Petersson's type for Fourier coefficients of Siegel cusp forms of degree 2 with respect to congruence subgroups, and as a corollary, show upper bound estimates of individual Fourier coefficient. The method in this paper is essentially a generalization of Kitaoka's previous work which studied the full modular case, but some modification is necessary to obtain estimates which are sharp with respect to the level aspect. 
Masataka Chida, Hidenori Katsurada, Kohji Matsumoto
math.NT