MANILA, Jan. 6 (XINHUA) -- Several firearms seized from the Ampatuan political clan, whose key members had been implicated in the November 23 massacre of 57 civilians in Maguindanao, came from the government arsenal, a senior Philippine military official said Wednesday.

Armed Forces of the Philippines Chief Gen. Victor Ibrado said 32 firearms and about 9 percent of the more than 1 million rounds of assorted ammunition seized from the family came from the government arsenal.

Ibrado said the serial numbers of some of the recovered firearms matched with firearms in the military inventory.

"This means that the (serial numbers of the) firearms that we recovered from them may be tampered," he said, quoting from the initial report that was submitted by the military's board of inquiry.

Ibrado told reporters in an interview that the board is still investigating how weapons belonging to the government arsenal ended in the Ampatuans' weapons cache.

"We want to find out who is supposed to be holding that firearm. If it's issued to him, he is supposed to be the one holding it. He should explain why it is now in the hands of the Ampatuan," he said.

Ibrado said he may submit next week an initial report to President Gloria Macapagal Arroyo, updating her on the progress of the investigation on the firearms and ammunition seized from the Ampatuans.