  A pure Dirac's framework for 3D Palatini's theory with cosmological constant
is performed. By considering the complete phase space, we find out the full
structure of the constraints, and their corresponding algebra is computed
explicitly. We report that in order to obtain a well defined algebra among the
constraints, the gauge group must be $SO(2,1)$. In addition, we obtain the
extended action, the extended Hamiltonian, the fundamental gauge symmetry, and
the Dirac brackets of the theory. Finally, we compare our results with those
reported in the literature.
