Athens, Greece ? In a major breakthrough against the elusive November 17 terror group, Greek police announced Thursday they captured a leader of the radical leftist organization and had confessions from three other members to bombings and shootings, including the assassinations of American and a British military attaches.

In all, said Police Chief Fotis Nassiakos, seven alleged group members were in custody, including leader Alexandros Giotopoulos the first arrests of November 17 members since the group emerged 27 years ago with the assassination of Richard Welch, the CIA’s station chief in Athens.

Since then November 17 has claimed responsibility for 22 other killings including four American officials, two Turkish diplomats and Greek businessmen and politicians and dozens of bomb and rocket attacks. Its last victim was British defense attache, Brig. Stephen Saunders, shot dead in June 2000.

Police penetrated the group as Greece came under increasing international pressure to improve security ahead of the 2004 Olympics. The governing Socialists have for years faced international criticism for failing to crack down on domestic terrorism. But authorities did not spell out how the group operated with impunity for more than a quarter-century.

State Department spokesman Richard Boucher declined to say if the United States would seek to extradite any of the suspects, but praised Greek efforts against the group.

Nassiakos told a nationally televised news conference that three of the suspects were brothers sons of a Greek Orthodox priest who served November 17 as executioners.

“This will clear a cloud that has been hanging over Greece. … This is a very great success for Greece and the government,” said Deputy Foreign Minister Yannis Magriotis.

November 17, which police estimate has fewer than a dozen members, was believed to have targeted Americans and their allies because of Washington’s backing of the Greek military dictatorship, which ruled from 1967 to 1974.

After the fall of the junta, left-wing and anti-American sentiment remained strong throughout the country and defined a generation of politicians, many of whom participated in the Nov. 17, 1973, student uprising from which the group took its name. The student opposition evolved, in part, into the Socialist Party that has governed Greece for 18 of the past 21 years.

Former U.S. government officials have alleged some Socialist party officials may have sheltered the group because of old student and radical ties.

November 17 has been on the State Department’s terrorism list since the 1980s. In its report to Congress last month, the State Department said Greece’s failure to arrest November 17 members was “troubling.”