It is widely held that terrorist group Hezbollah carried out the attack with Iranian backing, but Iran has consistently refused to co-operate with the investigation.
The case has been marked by accusations of cover-ups.

Mrs Kirchner is accused of signing a deal with Tehran to allow Iranian officials suspected of ordering the attack on the Jewish centre to be interviewed by Argentine magistrates in Tehran, rather than in Buenos Aires.
She is due to take her seat in Argentina’s Senate next week after crowning her political comeback with election victory in October. Her return to frontline politics would have given her immunity from prosecution on several separate corruption charges.
The Senate will now have to vote on lifting her immunity at the judge's request, for which a two-thirds majority is needed.