The Military Advocate General on Monday ordered the army's criminal investigations unit to investigate the death of a Palestinian protester who was killed by a tear gas canister at a demonstration in Bil'in in April 2009.

The Military Advocate General had refused to open a criminal investigation into the death of Bassem Abu-Rahma, but on Monday changed its mind after expert testimony showed that the tear gas canister was aimed directly at Abu-Rahma and was fired in violation of military orders.

The Military Advocate General notified Abu-Rahma's family and human rights lawyer Michael Sfard, who had planned to petition the High Court of Justice over the case.

The Israel Defense Forces first said Abu-Rahma was in a group of Palestinians hurling rocks at troops. But video footage showed him shouting, not throwing rocks, when he was shot.

Video footage filmed during the April 2009 protest against the separation fence in the Palestinian village of Bil'in also showed IDF troops firing tear gas canisters directly at demonstrators while in the presence of commanding officers.

Abu-Rahma's family welcomed the decision. "We are extremely happy that an investigation is finally being opened," said Ahmed Abu-Rahma, the victim's brother.

"This should have happened on the day [he was killed], and it is clear that the army opened the investigation because it was forced to, and that in the past year and a quarter it has tried to cover up the shooting of a non-violent protester that it had no reason to harm, let alone kill," Ahmed Abu-Rahma continued.

The original decision not to investigate Abu-Rahma's death ignored the video footage and relied on IDF solders' testimony that the tear gas canister hit wire along the separation fence and then ricocheted, striking Abu-Rahma. However, experts said that had the soldier who fired the canister followed IDF instructions, it would have landed hundreds of meters past where Abu-Rahma was standing.

Rights groups B'Tselem and Yesh Din said they were satisfied by the decision to probe the events surrounding Abu Rahma's death, but stressed that the delay in reaching the decision was unjustified.

"We hope the amount of time that has passed since the event won't affect the effectiveness of the investigation, and that today's decision by the Military Advocate General will bring justice to Abu-Rahma's family and the village of Bil'in," the groups said in a statement.

Sarit Michaeli of B'Tselem said the military informed the group on Monday of the decision. The military had no immediate comment.

Michaeli said there was no justification for the army taking 15 months to investigate the death, which she said was recorded on three video cameras.