Syrian Islamic radicals planted the bomb which exploded in late April in Damascus and sparked a bloody gun battle, the government has said.
The bomb shook diplomats used to the securities of a police state
The interior ministry said that a four-strong "isolated extremist fundamentalist group" had bombed a disused UN building in the capital.
In the subsequent battle, police killed two and captured the others while a passer-by and a policemen also died.
The ministry also linked the group to a robbery in a town south of the capital.
The blast on 27 April caused no casualties, but shook the diplomatic quarter.
Ayman Shilash Hasan, one of those killed in the shooting, had stolen the equivalent of about US $200,000 from the authorities in Qunaytera, a ministry official told the Syrian state news agency Sana.
The group bombed a finance department office in the town to cover up the crime on the same day they attacked the UN building in Damascus, 60 kilometres (40 miles) away, the official said.
The two surviving members of the group are in custody along with two "collaborators" arrested subsequently and arms and explosives from two caches in the Damascus area have been seized, he added.
Syria's secular authorities keep a tight lid on any internal Islamic unrest while maintaining strong Arab nationalist credentials abroad.