A comprehensive laboratory examination of two pieces of shrapnel retrieved from the bodies of Palestinians wounded in an explosion 12 days ago on a Gaza Strip beach, proves unequivocally that IDF artillery fire was not the cause of the blast, an internal military commission announced on Wednesday. Head of the commission Maj.-Gen. Meir Klifi said the two pieces of shrapnel retrieved from two Palestinians wounded in the explosion that killed seven and currently undergoing treatment at Soroka Hospital in Beersheba did not come from a 155 mm shell, the type of ordnance used by the IDF earlier that day in attacks on Kassam launch sites. The shrapnel lab results and other findings including the timing of the incident - according to the IDF the explosion occurred 10-15 minutes after artillery cannons stopped firing shells at a target next to the beach - conclusively exonerated the IDF, Klifi said, from responsibility for the blast. Klifi said that his investigative team had yet to determine the cause of the blast but did not rule out the possibility that it was caused by unexploded Israeli ordnance left lying on the beach weeks or even months ago. While the shrapnel did not match artillery shells fired by the IDF that day, it did, he said, match other types of ordnance in IDF use. "The examination of a second piece of shrapnel retrieved from the body of a boy who was wounded in the blast unequivocally shows that the explosion was not caused by a 155 mm artillery shell," Klifi told reporters during a press conference at Kirya Military Headquarters in Tel Aviv. "There is a possibility that the explosion was caused by unexploded Israeli ordnance and it is also possible that the blast was caused by an explosive device planted on the beach by Palestinian terrorists." Pieces of unexploded Israeli ordnance were sometimes used by terrorists in improvised explosive devices (IED), he said. IEDs are frequently used in attacks against IDF patrols along the Gaza Strip security fence and in the West Bank. The pieces of shrapnel, put on display for reporters, weighed each just a little over one gram. One of the pieces was extracted from the body of a girl wounded in the explosion early last week while the second piece was retrieved from a boy wounded in the blast last Wednesday. Both pieces were transferred into IDF custody and underwent a series of examinations and tests in the IDF Technological Unit's laboratories. The possibility that the explosion was caused by a 155 mm shell was ruled out, officials explained, since they did not bear any remnants of TNT explosives, the main composite in artillery shells.