We use a spectral sequence to compute twisted equivariant K-theory groups for the classifying space of proper actions of discrete groups.We study a form of Poincaré duality for twisted equivariant K-theory studied by Echterhoff, Emerson and Kim in the context of the Baum-Connes conjecture with coefficients and verify it for the group Sl 3 .Z/. 19L47; 55N91, 46L80In this work, we examine computational aspects relevant to the computation of twisted equivariant K-theory and K-homology groups for proper actions of discrete groups.Twisted K-theory was introduced by Donovan and Karoubi [9] assigning to a torsion element ˛2 H 3 .X; Z/ an abelian group ˛K .X / defined on a space by using finitedimensional matrix bundles.After the growing interest by physicists in the 1990s and 2000s, Atiyah and Segal [2] introduced a notion of twisted equivariant K-theory for actions of compact Lie groups.In another direction, orbifold versions of twisted K-theory were introduced by Adem and Ruan [1], and progress was made to develop computational tools for twisted equivariant K-theory with the construction of a spectral sequence by the authors, Espinoza and Uribe in [5].In [4], the first author, Espinoza, Joachim and Uribe introduce twisted equivariant K-theory for proper actions, allowing a more general class of twists, classified by the third integral Borel cohomology group H 3 .X G EG; Z/.We concentrate on the case of twistings given by discrete torsion, which is given by cocycles ˛2 Z 2 .G; S 1 / representing classes in the image of the projection mapUnder this assumption on the twist, a version of Bredon cohomology with coefficients in twisted representations can be used to approximate twisted equivariant K-theory, by means of a spectral sequence studied in [5] and Dwyer [10].