[en] The OPERA experiment at the Gran Sasso underground laboratory was designed to study ν_μ → ν_τ oscillations in appearance mode in the CNGS neutrino beam. In this paper we report the detection of the 5^th ν_τ candidate event found in the analysis of an enlarged data sample. Given the number of analysed events and the low background, ν_μ → ν_τ oscillations have been established with a significance of 5.1σ. The analysis of the present electron neutrino sample in the framework of the 3 + 1 sterile model is also presented. Finally the analysis of the muon charge ratio in the cosmic ray sample is discussed. (paper)