Necrophagous insects can be important tools in death investigations. In addition to their use in the estimation of post-mortem intervals, insects may serve as reliable alternate specimens for toxicological analyses in the absence of tissues and fluids normally taken for such purposes. Recent research has also demonstrated that the presence of drugs or toxins in decomposing tissues may alter the insect development rate when they using such tissues as food, thus potentially altering estimates of the post-mortem interval. Among the insects associated with decomposing body, Calliphoridae flies are the most abundant insects in this process. Chrysomya albiceps maggots were collected with forceps, deposited in plastic vials and transported to the laboratory in order to estimate the PMI (post mortem interval) of a victim found in the city of Campinas, SP, South-eastern Brazil, based on the estimated insect developmental time. In general, the immature insects are transported with the corpse to the morgue. However, the disaggregate behavior of the larvae and the disproportion of sizes among some specimens collected in different regions of the victim’s body have lead us to consider the possibility of drug overdose as the death cause. In this study, cocaine was detected on sections of second and third stage larvae by immunohistochemistry using the peroxidase-complex method. Positive specimens showed a more intense immunoreaction in an area located at the limit between exocuticle and endocuticle. These results constitute an evidence of cocaine accumulation in the cuticle of the larvae during their development. Neglecting the importance of this information may cause errors of up to12 hours in estimating the PMI.