The U.N.-backed Special Tribunal for Lebanon last year released the names of the four individuals wanted for the 2005 killing of Hariri, a former prime minister of Lebanon. They are: Salim Jamil Ayyash, Mustafa Amine Badreddine, Hussein Hassan Ainessi and Assad Hassan Sabra.
The four suspected members of Hezbollah are on trial in absentia. Ainessi's defense team, in a 28-page briefing, challenged the legality of the tribunal.
"The defense submits that the tribunal was not validly constituted, lacks the legitimate power to exercise a judicial function and therefore has no primary jurisdiction," the briefing read.
The defense team for Badreddine filed a similar appeal, asserting the U.N. Security Council overstepped its authority when it passed the resolution forming the court.
The tribunal is the first to use an international definition for terrorism. Badreddine's team said the Hariri assassination "did not constitute an armed conflict and it did not create any cross-border effects."
Hezbollah denies ties to the assassination and believes the matter is part of an Israeli plot. Badreddine was identified as the brother-in-law of Hezbollah commander Imad Mughniyeh, who was killed in 2008.
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