The decay events K3µ3 and Ke3 are investigated using the Lorentz invariance requirements as the restriction for the transition matrix, assuming that the weak Fermi interactions are participating in the decays. Fermi interaction concerned here is that realized among Λ(Σ), N, µ(e) and ν. The study of the experimental data in the light of the present analysis shows that Ke3 seems to have spin 0 and the tensor type of Fermi interaction is necessary, while for Kµ3 we can not draw any definite conclusion at present.