"Today's proceedings show that Lebanon, a proud founding member of the United Nations, is set for a course of judicial accountability through the rule of law," presiding judge Antonio Cassese said as the hearing opened before the Special Tribunal for Lebanon, based in Leidschendam near The Hague.
"This hearing signals an important moment for the life of the tribunal", the the world's first international court with jurisdiction over the crime of terrorism.
Cassese said that pre-trial judge Daniel Fransen had submitted 15 legal questions for the appeals chamber to clarify related to an indictment filed under seal by prosecutor Daniel Bellemare on January 17.
Fransen is tasked with confirming the indictment, widely believed to implicate the Lebanese Hezbollah group, before any arrest warrants can be issued for the 2005 bombing that killed Hariri and 22 other people in Beirut.
Among other things, he had asked the judges to decide how the crimes of terrorism, conspiracy and premeditated murder should be defined, and under which law -- Lebanese or international or both.
Neither the appeals judges nor the defence office have seen the indictment or the supporting evidence filed by the prosecutor.
Cassese said Monday's proceedings would help ensure a speedy trial, a prerequisite for fairness.
"Suspicions may have fallen on many", he said. "It is hence of vital importance that any person named in the indictment should know what charges they face."
"It is in the interests of Lebanon as a whole and world community at large that this process should move forward deliberately and expeditiously."
Cassese stressed the hearing was of a legal nature and would not deal with the facts of the case, but would allow the court to thrash out "a set of legal imperatives to deal with human tragedies".
"We will also have to discuss how the world community responds to one of the most widespread crimes of today, terrorism."
The prosecution and the defence office, created to protect the rights of defendants, both argued that the tribunal should apply only Lebanese law, which guides its operations, in defining terrorism.
"All necessary constituted elements of this offence are contained in the Lebanese law," said prosecutor Daniel Bellemare.
"There are no gaps or lacunae that need to be filled by reverting to international law. There is no agreed upon definition in international law on what constitutes the crime of terrorism."
The Lebanese criminal code defines terrorist acts as "all acts intended to cause a state of terror and committed by means liable to create a public danger such as explosive devices, inflammable materials, toxic or corrosive products and infectious or microbial agents."