Vanishing conjecture for the top cohomology of $\operatorname{SL}_n\mathbb{Z}$

Let $\operatorname{SL}_n\mathbb{Z}$ be the special linear group over the integers, and let $H^*(-;\mathbb{Q})$ denote rational group cohomology. Vanishing conjecture. $H^{\binom{n}{2}-i}(\operatorname{SL}_n\mathbb{Z};\mathbb{Q})=0$ for all $i<n-1$. This vanishing is presented as a consequence of the proposed stable instability and reflects torsion phenomena in the arithmetic group; the source gives no resolution.