Judicial sources said Wednesday that Maj. Gen. Jamil Sayyed, former head of general security, Maj. Gen. Ali Hajj, ex-chief of internal security forces, Brig. Gen. Raymond Azar, former military intelligence chief, and Mustafa Hamdan, the commander of the Republican Guards, were referred to further interrogation by Magistrate Elias Eid after being questioned by an international commission investigating Hariri's Feb. 14 assassination.
Eid, after questioning, could issue arrest warrants for further interrogation.
The sources said a fifth suspect, former legislator Nasser Kandil who was summoned for interrogation was released early Wednesday.
Beirut's leading daily An-Nahar quoted a senior security source as saying the international investigation commission chief, German prosecutor Detlev Mehlis, received important information from Syrian security officers who defected to a European country.
2014: The Year in Music [PHOTOS]