Thin right?angled Coxeter groups in some uniform arithmetic lattices

Using a variant of an unpublished argument due to Agol, we show that irreducible right-angled Coxeter group on n ? 3 ${n \geqslant 3}$ vertices embeds as thin subgroup uniform arithmetic lattice in indefinite orthogonal O ( p , q ) $\mathrm{O}(p, q)$ for some 1 $p, 1$ satisfying + = $p+q=n$ .