Will Titan sub victims' bodies ever be found? What were the banging sounds? And how WAS the OceanGate vessel still operating despite safety concerns? All questions still left unanswered as probe continues into tragedy

One year ago, the families of those onboard the Titan submersible were left with innumerable questions as to why their loved ones had gone missing and later confirmed to have died.

Those hoping for a trip of a lifetime included British billionaire Hamish Harding, OceanGate CEO Stockton Rush, French navy veteran PH Nargeolet and Pakistani businessman Shahzada Dawood and his son Suleman, who was just 19.

The Titan was taking the crew to see the wreckage of the Titanic 12,500 feet underwater at $250,000-a-head.

But the trip they were so excited for ended in tragedy. At first, concerns were raised about the missing submersible and panic ensued as rescuers raced to find the vessel before the oxygen ran out.

However, all that was found was debris and 'presumed human remains' as the Titan - owned and operated by OceanGate Expeditions - had presumably cracked under the deep-sea pressure. 

As the investigation into the devastating incident continues, MailOnline looks at what major questions remain unanswered a year later.

The Titan submersible had experienced several safety incidents on previous dives

The Titan sub is shown seconds before submerging with five people onboard

Five people were onboard, including British billionaire adventurer Hamish Harding (left) and Shahzada Dawood and his son Suleman (right), who is just 19

French Navy veteran PH Nargeolet (left) was in the sub along with Stockton Rush (right), CEO of the OceanGate Expedition

What caused the Titan to implode?

While most believe the hull collapsed as a result of enormous water pressure, it hasn't been conclusively decided whether 'cheap parts' were to blame.

Many experts think the materials used to construct the vessel could have cracked under the pressure, making a small indecision which would have widened and then 'crushed in less than a second'.

Last month, a new paper in the journal Proceedings of the National Academy of Sciences, suggested that microscopic imperfections in the hull could have contributed, leading to 'micro buckling' from the surrounding pressure.

What were the 'banging' sounds?

What were the 'banging' sounds that kept the hopes of families and rescuers alive in the search for the doomed Titan submersible?

After an agonising wait for news, late into the second day of searching, reports emerged that banging noises were detected in 30-minute intervals, deep under the ocean.

Played for the first time in a documentary, the hollow sound has a regular, steady beat which caught the attention of experts - and sparked hopes that the noise could be SOS signals being made by the five men on board.

According to experts, the 'banging' could have been from search equipment in the area, marine life such as whales or even just sounds from the depths of the Atlantic

'It could be somebody knocking, the symmetry between those knockings is very unusual,' former Navy Submarine Captain Ryan Ramsey told a documentary.

After the sound was first recorded at around 11.30pm on June 20, the US Navy confirmed that it had detected the noises the next morning.

Coast Guard Captain Jamie Frederick admitted at the time: 'With respect to the noises, specifically, we don't know what they are, to be frank with you.'

Tragically, hopes raised by the mysterious knocking sound were later dashed.

Have the bodies been found?

While 'presumed human remains' were located, there were no bodies found. 

The US Coast Guard said presumed human remains were carefully recovered from within Titan's debris and transported for analysis by medics.

Investigators carried out DNA tests on human remains found among the wreckage of the Titan submersible to try and identify who they belonged to.

Experts say the chances of recovering corpses are very slim, because the five men aboard the sub were almost certainly instantly obliterated when it imploded. 

Debris from the Titan submersible, recovered from the ocean floor near the wreck of the Titanic, is unloaded from the ship Horizon Arctic at the Canadian Coast Guard pier

Why the delay before sounding the alarm?

OceanGate Expeditions was criticised for taking eight hours to tell the US Coast Guard it had lost contact with Titan.

At 2.45pm - an hour and 45 minutes into the dive - it lost contact with its mothership, the Polar Prince.

But it wasn't reported as missing to the US Coast Guard until 10.40pm, eight hours later.

The company has not yet explained why it took so long to alert the Coast Guard when the Titan lost communications.

Dives to the Titanic usually take around eight hours, it is understood.

A file photo of the Titan submersible before its doomed voyage to the Titanic wreck last year

The Titan (above) suffered a deadly implosion last year that killed five people

Why wasn't the noise of the implosion flagged?

The U.S. Navy likely heard the sound of the Titanic tourist submersible imploding shortly after it was reported missing, according to a report - and yet still a massive international rescue effort was launched hoping to find survivors alive.

The Navy maintains an acoustic detection system around its coast for early detection of enemy submarines, and has done since the 1950s. 

'The U.S. Navy conducted an analysis of acoustic data and detected an anomaly consistent with an implosion or explosion in the general vicinity of where the Titan submersible was operating when communications were lost,' a senior U.S. Navy official told The Wall Street Journal in a statement previously.

A view of the Horizon Arctic ship, as salvaged pieces of the Titan submersible from OceanGate Expeditions are returned, in St. John's harbour, Newfoundland, Canada, June 28

'While not definitive, this information was immediately shared with the Incident Commander to assist with the ongoing search and rescue mission.'

The sound was detected in an area where the debris from the sub was located. Hours after the debris was found, officials noted the five people on board were presumed dead in an implosion.

The information about the possible implosion was 'immediately shared' with the Incident Commander.

But because the noise was 'not definitive at the point', the search and rescue mission continued.

Why did the Titan launch after concerns were raised? 

Experts in submersible vehicles wrote a letter warning trips on Titan could end in 'disaster' years before the vessel vanished.

The letter, obtained by the New York Times, warned that 'the current 'experimental' approach' of the company could result in problems 'from minor to catastrophic.

It was sent by the Manned Underwater Vehicles committee of the Marine Technology Society, a 60-year-old trade group.

It is unclear if any employee responded to the letter, and there was no further detail on why the approach was considered dangerous.

Anyone boarding Titan was required to sign a disclaimer that read: 'This experimental vessel has not been approved or certified by any regulatory body and could result in physical injury, emotional trauma, or death.'

On top of this, the Titan was hit by technical issues and mishaps on at least six previous occasions before it vanished. 

In August 2021, Arthur Loibl dived down 12,500 feet to the Atlantic wreck site and has said he was 'incredibly lucky' to survive the voyage.

Speaking to German tabloid Bild, the 60-year-old said parts fell off and the mission went into the water five hours late due to electrical problems.

Safety concerns included lighting and handles bought from DIY shops and no international safety certificate 

One hour and 45 minutes into the dive in the North Atlantic, off the coast of Newfoundland, the Titan lost communication with its support ship, the Polar Prince

At 9.45am - an hour and 45 minutes into the dive - it lost contact with its mothership, the Polar Prince. But it wasn't reported as missing to the US Coast Guard until 5.40pm, eight hours later

In July 2022, YouTuber Alan Estrada was onboard Titan when the batteries of the sub suddenly drained, forcing it to end early.

Mexican-born Estrada and his fellow submariners' time spent at the wreck was slashed from four hours to one so they could return to the surface before the sub lost power.

Meanwhile, Josh Gates told how the sub 'did not perform well' when he went on a trip to the Titanic in 2021.

He said: 'To those asking, Titan did not perform well on my dive. Ultimately, I walked away from a huge opportunity to film Titanic due to my safety concerns with OceanGate.

'There's more to the history and design of Titan that has not been made public - much of it concerning.'