From the FBI and CIA to intelligence committees in the House and Senate, the Aldrich Ames spy case presents investigators with a spider web of information to pull together.
No quick answers are likely.
But given the super-secret nature of Ames' work - and his 31-year career at the CIA - the damage is probably "massive," says former CIA official Vincent Cannistraro.
Of particular concern is Ames' mid-1980s assignment as chief of a counterintelligence branch in the Soviet-East European division. His job was to recruit spies for the United States and uncover enemy spies.
"That's where all the secrets are," says Pennsylvania State University historian Charles Ameringer, author of the book U.S. Foreign Intelligence.
Ames, accused of delivering U.S. secrets to the Soviet Union and Russia since 1985, could have used his spycatcher role to gain access to the names of most of the CIA's sources in the Soviet Union, Ameringer says.
The normal barriers set up for operational security - including "need to know" restrictions - are blurred for someone who was in Ames' sensitive position, he says.
Prospective sources, for example, would likely have been cleared through Ames to make sure they were not double agents.
U.S. intelligence specialists say they fear that if Ames betrayed those sources, the number of foreign agents executed by the Soviets could be in the double digits.
House Intelligence Committee Chairman Dan Glickman, D-Kan., insists it's far too early to determine how many lives may have been lost.
Some intelligence sources may have simply disappeared because they were spirited away to prison camps, Glickman says.
But the idea that the Soviets would retaliate against exposed agents by executing them is not far-fetched. "That's a pretty good assumption," Glickman says.
Among those whose deaths are suspected to be linked to the Ames case are KGB officers Valery Martynov and Sergei Motorin, reportedly convicted of treason and executed by the Soviets in 1986.
Another may be a Russian counterintelligence officer identified by the code name "GTPROLOGUE" in an affidavit filed in the Ames case.
Investigators also want to know what role Ames may have played in the decision by KGB officer Vitaly Yurchenko to return to the Soviet Union after a three-month defection to Washington in 1985.
Ames was among the U.S. intelligence officers who interrogated Yurchenko.
Investigators began suspecting Ames in 1991, and focused on him closely for the past year before arresting him Monday.
Former CIA officer Thomas Polgar says authorities wanted to avoid any legal weakness in their case, like those in the 1989 case of State Department officer Felix Bloch.
Although suspected of spying, Bloch was never charged.
"They didn't want to do that with this guy," says Polgar.
