Methylamine CH3NH2 is considered to be an important precursor of interstellar amino acid because hydrogen abstraction might lead to the aminomethyl radical •CH2NH2 that can react with •HOCO to form glycine, but direct evidence of the formation and spectral identification of •CH2NH2 remains unreported. We performed the reaction H + CH3NH2 in solid p-H2 at 3.2 K and observed IR spectra of •CH2NH2 and CH2NH upon irradiation and when the matrix was maintained in darkness. Previously unidentified IR spectrum of •CH2NH2 clearly indicates that •CH2NH2 can be formed from the reaction H + CH3NH2 in dark interstellar clouds. The observed dual-cycle mechanism containing two consecutive H-abstraction and two H-addition steps chemically connects CH3NH2 and CH2NH in interstellar media and explains their quasi-equilibrium. Experiments on CD3NH2 produced CD2HNH2, in addition to •CD2NH2 and CD2NH, confirming the occurrence of H addition to •CD2NH2.