After a normal preflight check had been carried out, the aircraft departed Bankstown. Soon after levelling off at 1500 ft the crew noticed an air noise from the left emergency exit which appeared to be partially dislodged. The pilot informed air traffic control of his intention to return to the airport but almost immediately the exit hatch separated from the aircraft. The aircraft landed without further incident. The design of the emergency exit release mechanism permitted the handle to be moved to the locked position while the forward latch remained unlocked. The preflight inspection involved viewing the position of the handle through a cutout in the handle cover to ensure that it was locked. While the pilot had completed this inspection, it provided no guarantee that the exit was properly locked because the pilot cannot see if the locking pins have located correctly. The investigation established that maintenance on the exit was not required, nor was it performed during the aircraft's last periodic inspection on 16 December 1993. The aircraft was not subsequently flown until the incident flight. However, on 29 December 1993 the operator reported that this aircraft may have been tampered with, together with two other aircraft belonging to him. Significant factors: 1. The emergency exit handle may have been moved by an unauthorised person or persons. 2. There was no means of alerting the pilot that the locking pins were not correctly located in the emergency exit locking mechanism. Safety Action: As a result of this investigation the Bureau issued the following Safety Advisory Notice: Safety Advisory Notice SAN 940101 The Bureau of Air Safety Investigation suggests that the Civil Aviation Authority consider the applicability of the provision of a suitable method(s) by which a pilot can obtain positive information on the locking status of the forward latching mechanism of the emergency exit in PA-44 aircraft. The Bureau also suggests that the Civil Aviation Authority ascertain whether a similar problem exists with other aircraft types.