BAN MOM, Laos — It was 100 miles downstream from China, on the banks of the Mekong River, where a notorious drug lord slipped ashore in the dusk into the hands of law enforcement.

Security officials from Laos arrested the trafficker, Naw Kham, but the international manhunt that led to his capture was organized in Beijing, by top Chinese government officials intent on making him pay for the killings of 13 Chinese seamen on the river, which has become a major trade route into China.

The bodies of the Chinese, the crew of two cargo boats, were found badly mutilated on the Thai side of the river in early October 2011. The killings, the worst slaughter of Chinese citizens abroad in recent memory, angered the Chinese public. Chinese investigators insist that Mr. Naw Kham was the mastermind of the murders.

China’s search for Mr. Naw Kham, overseen by its powerful Ministry of Public Security, was a hard-nosed display of the government’s political and economic clout across Laos, Myanmar and Thailand, the three countries of Southeast Asia that form the Golden Triangle. The capture shows how China’s law enforcement tentacles reach far beyond its borders into a region now drawn by investment and trade into China’s orbit, and where the United States’ influence is being challenged.