Let $Y (N) $ be the moduli scheme of dimension two principally polarized Abelian schemes with level $N$. It is claimed in "[G.Laumon - Fonctions zeta des variétés de Siegel](http://www.numdam.org/article/AST_2005__302__1_0.pdf)" (Lemma 4.1) that to an algebraic representation $W$ of $\mathrm{GSp}_{4}(\mathbb{Q})$ we can associate an $l$-adic smooth sheaf on $Y (N) [1/l] $.

Where can I find a proof of this please?