The analysis and interpretation of coincidence events in a Compton camera requires the comparison of the expected rates of observed events from sources with various emission rates, energy spectra and spatial distributions. Radioactive source distributions are often represented by the activity distributed among numerous voxels; each voxel having uniform internal activity and spectra within a cube. In this paper a mathematical model is constructed that predicts the expected rate of coincident Compton events from the rate of emissions from a single voxel source. This detailed model incorporates (1) the finite voxel size, (2) the blurring of the “Compton cone” by the limitations of energy resolution in the detectors and (3) the uncertainty in the Compton cone-axis due to the limited spatial resolution and ‘lever-arm’ separation between the coincident interactions. The resultant rates can be used to generate the system response matrix for source reconstruction and, therefore, are directly applicable in list-mode MLEM source reconstruction algorithms.