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In this paper, we describe a 4π Compton imager composed of a single 15 mm × 15 mm × 10 mm CdZnTe detector. Full 4π images are reconstructed via list-mode maximum likelihood (ML). A new weighting method for ML reconstruction is proposed in which the contributions of small-uncertainty sequences are enhanced relative to sequences with large uncertainties. The new reconstruction method is compared with traditional ML techniques for measured imaging data. The 4π Compton imager has a measured intrinsic imaging efficiency of nearly 2% and an imaging resolution using the weighted ML reconstruction method of 17° at 662 keV after 10 iterations.