WASHINGTON — One of the shredded documents the FBI says it recovered from Chi Mak's trash seemed to be a set of instructions. Machine printed, in Chinese, it urged Mr. Mak - an engineer for a California defense firm and a naturalized US citizen - to attend more seminars on special subject matters. It went on to list technologies of interest to its unnamed author, including torpedoes, aircraft-carrier electronics, and a "space-launched magnetic levitational platform."
The second document, also in Chinese, was handwritten. It was a list of nine related naval technologies, including ship propulsion - Mak's expertise.
Innocent notes, or evidence of something sinister? The latter, according to the FBI. Late on Oct. 28, agents burst into Mak's modest Downey, Calif., home and arrested him and his wife, Rebecca Laiwah Chiu. At the same time, agents detained Mak's brother, Tai Wang Mak, a Chinese national, as he waited at Los Angeles International Airport for a flight to Hong Kong.
Thus one month ago US officials rolled up what they allege to be a family spy ring, linked to the country some American officials call the most active collector of intelligence in the US today: the People's Republic of China.
China has spent more than two decades creating a large and varied intelligence infrastructure in the United States, according to US counterintelligence documents. High-profile prosecutions in recent years related to alleged Chinese espionage may merely hint at the depth and breadth of China's collection efforts.
It isn't a classical KGB-like operation, featuring dead drops and microfiche passed in the night. China's espionage style is unique, according to US law enforcement. It depends on a multitude of relative amateurs: Chinese students and visiting scientists, plus people of Chinese heritage living in the US.
Each individual may produce only a small bit of data. But collectively the network might vacuum up an extensive amount of sensitive military and economic information.
"To the extent we suffer losses against China, typically we suffer them day in and day out on a modest scale of operation," says Paul Moore, who was the FBI's chief China analyst for more than 20 years.
According to an affidavit filed in federal court late last month, Chi Mak was born in China. He and his wife became naturalized US citizens in Los Angeles in June 1985.
At the time of his arrest Mak worked as a principal support engineer at an Anaheim, Calif., defense firm named Power Paragon, leading an effort to develop a new electric-drive submarine propulsion system.
His brother Tai Mak is a Chinese citizen who entered the US legally on May 22, 2001. He works as broadcast and engineering director for Phoenix North American Chinese Channel, a satellite television service that provides Chinese-language programming in the United States.
Law-enforcement officials allege that Chi Mak took computer disks containing sensitive information from his workplace, and then passed the information to his brother, who duplicated it on his own disk in encrypted files.
Tai Mak was allegedly carrying this data when he was arrested Oct. 28.
An FBI agent has said in court documents that Chi Mak has admitted passing information to China for years.
However, the members of this purported family spy ring have not been charged with espionage. Rather, they've been indicted on a charge of being unregistered agents for a foreign government.
All three have pleaded not guilty. Ms. Chiu is free on a $300,000 bond. The Mak brothers have been denied bail.
An attorney for Tai Mak, John Early, told a judge at a hearing Monday that the FBI rushed forward with an incomplete case when it learned that Tai Mak and his wife were flying out of the country.
"The grandiose allegations suddenly seem smaller and smaller," said Mr. Early.
It's certainly true that in recent years the US government has run into trouble when prosecuting cases of alleged espionage involving China.
Six years ago the US accused Los Alamos National Lab scientist Wen Ho Lee of stealing nuclear secrets for China. He eventually pleaded guilty to a lesser charge of mishandling computer files. His case became a rallying point for many in the Chinese-American community who felt he was being targeted because of his ethnic heritage.
This January a federal judge, citing what he felt was prosecutorial misconduct, threw out charges of taking classified documents filed against Katrina Leung, a Chinese-American civic leader in California. Ms. Leung was a paid FBI informant whom prosecutors suspected was also passing information to China.
But former and current counterintelligence officials insist that the collapse of these cases does not mean that they are targeting a nonexistent threat. China is one of the top five intelligence collectors in the US, if not the top one, they say.
And China's methods are different than those used by other nations eager to glean US secrets, say experts. In some ways that makes them more difficult to counter.
Recent cases involving the People's Republic of China (PRC) "are just the tip of the iceberg of an already-large and increasingly capable PRC intelligence effort," concludes a US government Intelligence Threat Handbook, an unclassified manual for security officers produced by an arm of the National Security Agency.
According to this document, Beijing does not favor the classical methods used by other big intelligence services, featuring tight control over a few, deeply buried and valuable agents.
Instead, it employs a vast, decentralized network that employs Chinese students, businesspeople, and delegations in the United States, and targets Americans of Chinese ancestry as possible espionage recruits.
Chinese factories and research institutes eager for US economic or military information often concoct and control their own collection schemes.
Intelligence officials in China may pass along possible contact names to a scientific team traveling to the US, for instance. The Chinese scientists may then make a direct appeal for help - or invite the US contact for a reciprocal visit to China, where they can be tired out with banquets and visits and then swarmed by questioners, in hopes of eliciting an unguarded comment.
Chinese human-intelligence operations "primarily rely on collecting a small amount of information from a large amount of people," says the Intelligence Threat handbook.
The Chinese-American community is the target of an estimated 98 percent of recruitment efforts by China's equivalent of the CIA, the Ministry of State Security, according to the handbook.
Chinese intelligence aims its efforts at Chinese-Americans because it feels it can make an effective approach to them - not because it considers them more vulnerable than other ethnic groups.
The crux of the Chinese approach is to appeal to an individual's desire to help out China in some way. "Whatever the reason, ethnic targeting to arouse feelings of obligation is the single most distinctive feature of PRC intelligence operations," concludes US counterintelligence.
In some ways, the alleged misdeeds of the Mak brothers are not typical of the Chinese approach, according to Mr. Moore, the former FBI China analyst.
The torn-up lists of technologies that the FBI claims to have taken from Chi Mak's garbage would be evidence of more direct control than Chinese agents typically have, says Moore. "Usually what you see is a Chinese-American fellow on this side just making it up as he goes along."
In court FBI agents have struggled to explain why the case against the Maks doesn't include espionage charges. The government says it's not clear the information on the disk or disks allegedly found in Tai Mak's possession is, in fact, classified. It may be sensitive data that are unclassified but banned from export to other countries.
News reports have described information about sensitive weapons that Chi Mak may have been passing to China for years, but the US government has not publicly made such sweeping allegations.
Clearly, however, the FBI has had Chi Mak under surveillance for at least a year, if not longer. Electronic eavesdropping equipment was salted throughout his house. At one point, Chiu said to her husband that the "things" his brother was asking him to take "are certainly against the law," states an FBI affidavit.
Five days later all three were arrested.