The judge in charge of the Vladimiro Montesinos case announced she would call for testimony from CIA Director George Tenet and Robert Gorelick, the CIA Lima station chief in 1999.
Montesinos, the former right-hand man of disgraced president Alberto Fujimori, went on trial at the El Callao naval base just west of Lima.
He is charged with allegedly helping to smuggle 10,000 machine guns to the Revolutionary Armed Forces of Colombia (FARC), Latin America's largest insurgency.
If convicted, the former spy chief may face 20 years in prison.
Judge Ines Villa announced she wanted Tenet to testify after a request from Estela Valdivia, Montesinos's defence lawyer. According to court sources, Tenet might testify either by questionnaire or via teleconference.
Ronald Gamarra, the country's anti-corruption prosecutor, said he believed Montesinos had support from the CIA in the arms deals.
Prosecutors did not have "solid proof" of the connection, Gamarra said in a weekend interview with the daily El Comercio. However, there were "many indications that could prove this relationship."
Montesinos' goal was to "ingratiate himself once again with the CIA," which at the time was attempting to "radicalise the fight against the FARC," Gamarra told the newspaper.
Gamarra however bemoaned the CIA's failure to help out in this investigation, "despite the requirements of Peruvian law."
Anti-corruption prosecutor Luis Vargas told Colombian radio network RCN there was information showing that CIA agents collaborated with Montesinos in the gun smuggling operation.
According to the charges, Montesinos, with the backing of Fujimori's government, formed a criminal organisation that bought at least 10,000 AKM machine guns in Jordan.
Peruvian army officers - or agents posing as army officers - completed the purchase. But instead of going to Peru, the guns were air dropped into FARC-controlled territory in southern Colombia in the first half of 1999.
Montesinos kept silent throughout the day, much as he has done during his five other trials. He has yet to face charges of illegal enrichment, human rights violations and money laundering.
The court will also decide on the fate of 37 other people, including former military officers, a number of Ukrainians - and French national Charles Acelor, extradited to Peru from Germany just over one year ago.