The photodissociation dynamics of diiodomethane molecules has been investigated in the wavelength range of 277-305 nm by an ion imaging spectrometer operated under optimal conditions for velocity mapping, where the ions were generated from (2+1) multiphoton ionization of I(P-2(3/2)) and I*(P-2(1/2)) fragments with the same laser as that to dissociate the parent molecules. The speed and angular distributions of I* and I fragments were determined from the images. The translational energy distribution of I*(P-2(1/2)) fragment consists of a single Gaussian component (named G*), while that of I(P-2(3/2)) consists of two Gaussian components (named G1 and G2). It was found that the component G* and G2 show similar angular distributions and similar fragmentation energy partitioning ratios, indicating that these two components originate from dissociation at the same electronically excited state, while the component G1 is from another state. Three fragmentation pathways were employed to account for the experimental observations, the adiabatic dissociation from the 1B(1) state to form I(P-2(3/2)) with component G1, the adiabatic dissociation from the 2B(1) state to form I*(P-2(1/2)) with component G*, and the nonadiabatic dissociation from the 2B(1) state caused by coupling with the higher 2A(1) state to form I(P-2(3/2)) with component G2.