Non abelian Reidemeister torsion and volume form on the SU(2)-representation space of knot groups

For a knot K in $S^3$ and a regular representation $\rho$ of its group $G_K$ into SU(2) we construct a non abelian Reidemeister torsion on the first twisted cohomology group of the knot exterior. This non abelian Reidemeister torsion provides a volume form on the SU(2)-representation space of $G_K$. In another way, we construct according to Casson–or more precisely taking into account Lin’s and Heusener’s further works–a volume form on the SU(2)-representation space of $G_K$. Next, we compare these two apparently different points of view–the first by means of the Reidemeister torsion and the second defined ``a la Casson"–and finally prove that they define the same topological knot invariant.