Eugene Wigner, On unitary representations of the inhomogeneous Lorentz group, Annals of Mathematics, 40 (1939) 149–204

The observation that Wigner’s representations $U_{(-)}$ are those for which all the maps $g \mapsto \langle \Phi \vert U_g \Psi \rangle$ are measurable and their correspondence of irreducible unitary representations to induced representations of irreps of the stabilizer group of a given momentum is (e.g. Dragon 16) due to

George Mackey, Induced Representations of Groups and Quantum Mechanics, W. A. Benjamin, New York, 1968

Review:

Bert Schroer, Wigner Representation Theory of the Poincaré Group, Localization, Statistics and the S-Matrix, 1996 (pdf)