  We prove that the group of normalized cohomological invariants of degree 3
modulo the subgroup of semidecomposable invariants of a semisimple split linear
algebraic group G is isomorphic to the torsion part of the Chow group of
codimension 2 cycles of the respective versal G-flag. In particular, if G is
simple, we show that this factor group is isomorphic to the group of
indecomposable invariants of G. As an application, we construct nontrivial
cohomological classes for indecomposable central simple algebras.
