[en] The authors analyze the energy spectrum and time dependence of the 50 MeV to 2 GeV gamma rays observed from the 1991 June 11 solar flare. It is shown that the emission detected at the late phase of this flare with EGRET on the COMPTON Observatory can be best explained by a model in which the bulk of the particles were accelerated during the impulsive phase and subsequently trapped in a coronal magnetic loop. The authors fit the observed spectrum with a combination of pion decay radiation and primary electron bremsstrahlung. The trapping of the ions and relativistic electrons in the loop on time scales of hours requires that the level of the plasma turbulence and strength of the ambient coronal magnetic field be sufficiently low. The comparison of the 1991 June 11 data with data available for the 1982 June 3 and 1991 June 15 flares indicates that all three of these flares probably produced pions under similar conditions