Swiss authorities are cooperating with a number of countries, among them Haiti, Egypt, Tunisia and Ukraine, to return stolen assets that have been frozen following changes in power, Zellweger said.
Specifically, they are working to return $40 million to Tunisia, a "big slice" of the $60 million stashed during the era of former leader Zine al-Abidine Ben Ali, he said.
But the killing of Egypt's general prosecutor has slowed cooperation with Cairo on returning funds linked to former President Hosni Mubarak, he said.
The two houses of the Swiss parliament still need to reconcile their versions of the new draft law, including the issue of a statute of limitations, Zellweger said.
"I guess that we will only have the statute by the end of the year," he said. "It will be the most comprehensive act worldwide ... it is the right thing to do."
In the last 25 years, Switzerland has returned $1.8 billion in stolen or embezzled funds seized in accounts held by dictators ranging from the Philippines' Ferdinand Marcos and Nigeria's Sani Abacha to Haiti's Jean-Claude 'Baby Doc' Duvalier and Sese Seko Mobuto of the former Zaire.
It was reported earlier that Switzerland complied with Ukraine's request to legally assist Ukraine regarding blocked funds of former Ukrainian president Viktor Yanukovych.