Pneumopericardium (PPC) and Tension Pneumopericardium (TPPC) refer to collections of gas in the pericardial cavity, the latter resulting in air tamponade and cardiac compromise. Following penetrating chest injuries, PPC and TPPC appear to be uncommon findings associated with a high mortality and correlated with other thoracic trauma. Diagnosis of PPC and TPPC is difficult relying on conventional autopsy alone, while postmortem computed tomography (PMCT) shows a high sensitivity for the detection of internal gas collections. Possibly due to difficulty in detection, PPC and TPPC have not been discussed from a forensic point of view and many lethal cases of PPC and TPPC might have been missed in medicolegal investigations. In this report, we present a case with suicidal, penetrating stab wounds to the chest resulting in a TPPC with lethal air tamponade documented by PMCT.