Thailand's top army commander said on Thursday some of the bullets used in an assassination attempt on the leader of the “yellow shirt” protest movement came from an army training facility. Army chief Anupong Paochinda said he had ordered a probe into the three M-16 bullet casings found at the scene of last Friday's attack on Sondhi Limthongkul, whose movement occupied Bangkok's main airport last year. “These bullets are for training purposes by the First Region Army. This is clearly a leak,” Anupong told reporters, confirming reports in the Thai media. Anupong has previously denied speculation by some of Sondhi's colleagues that military personnel may have been involved in the assassination attempt. Police have made no arrests since the dawn attack by at least five gunmen who raked Sondhi's car with automatic rifle fire as he was being driven to a radio station. Police found 84 spent cartridges and an unexploded M-79 grenade at the scene of the attack, which followed a week of violent street protests by a rival group that supports former premier Thaksin Shinawatra. Sondhi, a core leader of the People's Alliance for Democracy (PAD) which led mass protests against Thaksin before he was ousted in a 2006 coup, was expected to leave hospital on Friday. The media maverick has been silent while recovering from a head wound doctors said was not life-threatening. Some PAD members believe elements of the military may have been involved in the attack, which also seriously wounded Sondhi's driver. “If Anupong does not get serious and investigate those bullets, we will consider him an accomplice,” PAD co-leader Somsak Kosaisuk told Reuters. The PAD played no part in last week's political violence which left two people dead and disrupted a summit of Asian leaders after Thaksin supporters invaded the meeting site. Foreign Minister Kasit Piromya, who is visiting the United States this week, accused Thaksin of playing a role in the attempt on Sondhi's life. “Thaksin failed on the populist movement and now I think he has resorted to some sort of assassination attempt,” the Bangkok Post quoted Kasit as telling a group in New York. Kasit, criticized for backing the PAD's occupation of Bangkok's airports last year as part of its campaign against a pro-Thaksin government, gave no evidence to support his claims. Thaksin, a telecoms billionaire before entering politics, has lived in self-imposed exile to avoid a two-year jail term on conflict of interest charges. The Thai government stripped Thaksin of his passport last week, when it also emerged that the wily former premier had received a diplomatic passport from Nicaragua, which named him a “special ambassador”. The government has issued several arrest warrants for Thaksin and lobbied foreign countries to stop giving him refuge.