Aquino, 40, admitted receiving classified US government documents from Filipino-American Leandro Aragoncillo, then an intelligence analyst of the Federal Bureau of Investigation, from January to September 2005.

Aquino, a close aide of Sen. Panfilo Lacson who was then head of the Philippine National Police under President Joseph Estrada, has been linked to the Kuratong Baleleng massacre and also with the murder of publicist Salvador Bubby Dacer and his driver, Emmanuel Corbito. He and another co-accused fled the country when Estrada was deposed.

The US initially alleged that Aquino received US government documents from Aragoncillo, a Filipino American, which he later passed on to Philippine officials, including Sen. Panfilo Lacson, Estrada, former House Speaker Arnulfo Fuentebella and others.

“Aquino is now an admitted spy, who cultivated and used Aragoncillo, a willing accomplice, to transfer US intelligence secrets abroad,’ said US Attorney Christopher J. Christie.

“He [Aquino] did this at the behest of a high-level government official in the Philippine legislature. We view that as a grave intrusion on the integrity of our national security, and we will seek the longest prison sentence possible for Aquino," he added.

Having pleaded guilty, Aquino avoided a more serious charge of espionage and a possible life sentence. Legal experts said that with the plea bargain, Aquino could face a minimum term of three to six years.

The plea spared the US government a trial that would have detailed how classified documents were pilfered from the White House and the FBI.

Investigators said Aragoncillo passed on the documents to opposition politicians in the Philippines, including Estrada, Lacson, and Fuentebella.

The three were not indicted as co-conspirators in the espionage case.

The FBI arrested Aragoncillo and Aquino in September last year. Aragoncillo late last year pleaded guilty to the charges and will be sentenced soon. Aquino will be sentenced in October.

In Manila, meanwhile, the Philippine justice department, who has been seeking the extradition of Aquino, said the guilty plea will result in delay of the pending cases against him.

Justice Secretary Raul Gonzales said the Philippines will wait until Aquino completes his sentence in the United States.

 Lacson, reacting to Aquino’s admission of guilt, noted that the charges of conspiracy and acting as a foreign agent against Aquino had been dropped, meaning that there was no conspiracy to pass on information to foreign government officials.

In an interview with the Philippine Daily Inquirer, Lacson said this practically absolved himself and Estrada from charges of having conspired in the theft of the classified US documents.

“The charges of conspiracy and acting as a foreign agent were dropped, which means that no other persons will be charged any further in relation to him," Lacson told the Inquirer.

“It is now clearly established that there was no conspiracy and that nobody hired Aquino to act as a foreign agent,’’ he added.

In a later interview with reporters, Lacson stressed that the “receiving and keeping" of classified information was “personal” to Aquino.

Lacson also said he did not influence Aquino to make the guilty plea, stressing this was his “own personal decision.”