Lebanon is poised to mark the second anniversary of the Beirut port explosion which killed at least 215 people, wounded thousands and damaged large swathes of the capital.

Despite the devastation wrought by the blast – one of the biggest non-nuclear explosions ever recorded – a judicial investigation has brought no senior official to account.

With the probe frozen for months, many Lebanese see this as an example of the impunity enjoyed by a ruling elite that has long avoided accountability for corruption and bad governance, including policies that led to a financial collapse.

Here is a recap of how the blast happened, and the obstacles that have paralysed the investigation.

What happened?

The explosion just after 6pm on August 4, 2020, resulted from the detonation of hundreds of tonnes of ammonium nitrate which ignited as a blaze tore through the warehouse in which they were stored.

Originally bound for Mozambique aboard a Russian-leased ship, the chemicals had been at the port since 2013, when they were unloaded during an unscheduled stop to take on extra cargo.

The ship never left the port, becoming entangled in a legal dispute over unpaid port fees and ship defects.

No one ever came forward to claim the shipment.

The amount of ammonium nitrate that blew up was one fifth of the 2754 tonnes unloaded seven years earlier, the FBI concluded, adding to suspicions much of the cargo had gone missing.

The blast was so powerful it was felt 250 kilometres away in Cyprus and sent a mushroom cloud over Beirut.

Who knew about the chemicals?

Senior Lebanese officials, including President Michel Aoun and then-prime minister Hassan Diab, were aware of the cargo.

Mr Aoun said shortly after the blast he had told security chiefs to “do what is necessary” after learning of the chemicals.

Mr Diab has said his conscience is clear.

Human Rights Watch said in a report last year high-level security and government officials “foresaw the significant threat to life … and tacitly accepted the risk of deaths occurring”.

Who has investigated the blast?

The justice minister appointed Judge Fadi Sawan head investigator shortly after the blast.

In December 2020 Judge Sawan charged three ex-ministers and Mr Diab with negligence over the blast, but then hit strong political pushback.

A court removed him in February 2021, after two of the ex-ministers – Ali Hassan Khalil and Ghazi Zeitar – complained he had overstepped his powers.

Judge Tarek Bitar was appointed to replace Judge Sawan.

He sought to interrogate senior figures including Mr Zeitar and Mr Khalil, both members of Parliament Speaker Nabih Berri’s Amal Movement and allies of the Iran-backed Hezbollah.

He also sought to question Major-General Abbas Ibrahim, head of the powerful General Security agency.

All have denied wrongdoing.

How has the probe been stymied?

All of the current and former officials Judge Bitar has sought to question as suspects have resisted, arguing they have immunity or that he lacks authority to prosecute them.

This tussle has played out in the courts, in political life and on the streets.

Suspects swamped courts last year with more than two dozen legal cases seeking Judge Bitar’s removal over alleged bias and “grave mistakes”, leading to several suspensions of the investigation.

The ex-ministers have said any case against them should be heard by a special court for presidents and ministers.

That court has never held a single official accountable, and it would pass control of the probe to ruling parties in parliament.

The investigation has been in complete limbo since early 2022 due to the retirement of judges from a court that must rule on several complaints against Judge Bitar before he can continue.

The finance minister – who is backed by Mr Berri – has held off signing a decree appointing new judges, citing concerns with the sectarian balance of the bench.

What does Hezbollah think?

Judge Bitar has not pursued any members of the heavily armed, Iran-backed Hezbollah group.

But Hezbollah campaigned fiercely against him last year as he sought to question its allies.

One senior Hezbollah official sent Judge Bitar a message warning the group would “uproot” him.

An anti-Bitar protest called by Hezbollah and its allies in October escalated into deadly violence.

Hezbollah has accused the United States, which lists the group as a terrorist organisation, of meddling in the probe. The US ambassador has denied this.

Hezbollah dismissed accusations made at the time of the blast that it had stored arms at the port and says it had nothing to do with the blast.

Its adversaries have long accused the group of controlling the port – something it also denies.