CAMBODIA'S police have arrested Patrick Devillers, a French architect linked to Bo Xilai. Until recently Mr Bo was a senior member of China's Communist Party, whose sacking, amid allegations of widespread corruption in Chongqing province, has sent political shockwaves across China and throughout the region. Mr Devillers had been identified as one of only two foreigners to belong to Mr Bo's inner circle—and the only one who is still alive.

The police confirmed that Mr Devillers was taken into custody on June 13th following a request from China, but no charges had been laid. The French embassy is seeking a clarification about his arrest, which was made amid a series of high-level talks between diplomats in Beijing and Phnom Penh.

Their meetings resulted in loans worth $430m, issued mainly through China's Export-Import Bank (Exim), after negotiations which were concluded in Phnom Penh by the prime minister, Hun Sen, and He Guoqiang, a member of the Chinese Politburo's Standing Committee.

The funds are earmarked for the construction of a dam near the north-west town of Battambang and for the extension and widening of two highways. The deal marks an acceleration of China's investment programme in Cambodia, which has already raised the fear of chequebook diplomacy among Cambodia's more China-wary neighbours.

Mr Bo, once the Communist Party's leader in Chongqing province, was sacked in April after his police chief, Li Wangjun, fled to an American consulate. Mr Li is reported to have revealed to the Americans his suspicion that Mr Bo's wife, Gu Kailai, was involved in the death of a British businessman, Neil Heywood, with whom Chongqing's power couple was closely affiliated.

Ms Gu has since been named as a suspect in Mr Heywood's death. Further investigations have revealed systemic corruption in Mr Bo's domain as well as the abuse of power on a breathtaking scale within the Communist Party ranks he controlled. The lurid allegations ranged against Mr Bo and his colleagues have ranged from kidnap and torture to extortion and high-end prostitution rackets.

Exactly why Mr Devillers is wanted has not been made clear. Cambodian police declined to comment further and the French embassy in Phnom Penh asked that questions concerning the case to be asked by e-mail. They have yet to reply with an answer.

Mr Devillers lived in Phnom Penh for about six years and acquired a plot of land near Kep, an old French-colonial beachside town near the Vietnamese border. He had avoided journalists, declining to comment on reports that he and Ms Gu were partners in setting up a British company to select European architects for projects in China.

Described as a quiet man and a devout Taoist, Mr Devillers apparently ignored friendly warnings that he might face arrest in his adopted homeland, given the Cambodian government's close relationship with China. Cambodia ratified an extradition treaty with China in June 2000.

Mr Devillers's arrest has raised questions beyond the mystery of his criminal case. In Cambodia it draws particular attention to the influence of the Chinese state, which has become the biggest donor and lender within a crowded field. Another package of loans worth $302m had been signed in February. China's total investment since 1994 has been estimated at almost $10 billion.

John Brinsden, the vice-chairman of ACLEDA, a private bank in Cambodia, noted that Chinese investments in infrastructure like bridges and roads have become prominent over the past five years and that China's government is now giving as much in direct aid as an organisation of donors that represents mainly Western countries. Before Mr Devillers's arrest was known, Mr Brinsden had said that “of course, as is always the case, [China's aid] comes with a price and the price is that Cambodia must remain welcoming to Chinese investors who do, one suspects, get the pick of the bunch when it comes to investment licences.”

This matters to the neighbours too. Cambodia is currently acting as the chair of the Association of South-East Asian Nations (ASEAN). Its readiness to toe Beijing's line over issues like the Spratly Islands has caused consternation within the trade organisation, especially in places like Vietnam and the Philippines, which would prefer that ASEAN present a united front in the dispute over resource-rich shoals in the South China Sea.

Cambodia courted international controversy three years ago when it bowed to a request from Beijing and deported 20 ethnic Uighurs who had been seeking asylum following a crackdown in China's far west. Likewise in 2002 human-rights groups were outraged when Cambodian police seized two Falun Gong members who had been living here under the protection of the United Nations and deported them back to China. Mr Devillers seems to be coming late to a lesson that others have learned before him: the distance between the People's Republic of China and Hun Sen's Cambodia is not so great at all.