To date, no one has been held responsible for the explosion, which was caused by an unattended stock of ammonium nitrate left unsafely in Beirut's port. Over 200 people were killed, and neighborhoods across the capital were devastated.

Officials knew that the highly explosive substance had been in the port, in close proximity to residential areas, for years, and there have been widespread calls for those responsible for the disaster to be held to account.

But the inquiry has been repeatedly delayed. In February, Bitar's predecessor was removed by a court after he charged Diab and three former ministers with "negligence and causing death to hundreds" in the explosion.

Members of different political factions have previously criticized Bitar; the Shiite group, Hezbollah, has accused him of "politicizing" the inquiry, while a group of former prime ministers wrote a letter after the Diab was issued with the August subpoena, saying it was "a dangerous precedent and a deliberate measure that undermines the position of the prime minister".