Caitlin Wilson
Live editor

We've been hearing from OceanGate co-founder Guillermo Sohnlein today as US Coast Guard hearings into the Titan sub disaster enter their second week.

Here's what we've learned:

• Investigators asked Sohnlein what the original vision for OceanGate was. He said it was to create a fleet of deep-diving submersibles capable of carrying five people and available for charter anywhere in the world.
• When Sohnlein and CEO Stockton Rush began working, together he said the pair had "no intention of creating our own subs".
• He said it was a logistical choice to leave OceanGate in 2013, and that the company could use his salary to hire engineers or other specialists.
• Sohnlein declined to advise the best way to regulate sub, saying the topic was not in his "wheelhouse".
• We also learned Sohnlein had never been on an OceanGate dive himself, saying he didn't want to take up room from paying customers.
• In his closing remarks, Sohnlein said he wasn't sure if "we'll ever know the answers to all of this", but expressed his hope that this "can't be the end of deep ocean exploration".

There are more witnesses expected later today, but we are closing our live coverage of the hearing for now.

The writers for this page have been Rebecca Morelle and Ana Faguy. It has been edited by me. Thank you for joining us.

You can catch up with more of our coverage of the Titan sub investigation below:

Boss of Titan sub firm said: 'No-one is dying under my watch'

Crew's final words and new footage of wreck: Key takeaways from Titan sub hearings

'All good here': Titan sub's last messages before implosion

New Titan footage shows wreckage of destroyed hull on sea floor

We've just concluded the questioning of Guillermo Sohnlein, one of OceanGate's co-founders.

He was the first witness during the second week of pubic hearings on the 2023 Titan sub disaster.

Today's proceedings are expected to continue with two more witnesses, and the hearings will continue through the week.

Image source, US Coast Guard

Sohnlein is giving his closing remarks to investigators.

"This was not supposed to happen, this should not have happened," he says of last year's disaster that saw all five people on board the Titan killed.

"I don't know what happened," he adds of that incident.

Sohnlein says he doesn't know who made what decision and how that led to the tragedy.

"I don't know if we'll ever know the answers to all of this," he says.

I hope more people experience submersibles like this but "it looks like OceanGate will not be a part of that", he says.

Sohnlein says this incident "can't be the end of deep ocean exploration" and says he hopes study of the depths of the ocean continues and can even become available to the general public.

Sohnlein says Rush asked him every year to come on one of the submersible dives, but he declined every time.

"As a shareholder I never wanted to take up room on the dive," he says.

We were not motivated by tourism, we were motivated by exploration, Sohnlein says.

"I wanted to make room for people like Renata," he says referencing a passenger who testified last week about her long desire dream to visit the remains of the Titanic, which she did with OceanGate.

An investigator asks Sohnlein the best way to regulate subs, but he brushes off the question.

"I don’t know what the right way is to regulate this kind of activity," Sohnlein says, adding the topic is not in his "wheelhouse".

He says given the number of submersibles in the world - he estimates there are at most 100 - there isn't a need for new regulations, calling it a potential "waste of taxpayer money".

Richard Gray
Editor, BBC Future

Image source, Reuters

The wreck of the Titanic lies in total darkness on the seabed, nearly 2.4 miles (3.8km) below the surface.

It is an incredibly hostile environment that makes visiting the wreck a challenge.

Travelling that deep can take time – it is a two-hour-long descent. Below about 3,300ft (1,000m), sunlight is unable to penetrate the water and everything exists in what is aptly named the "midnight zone". It makes it easy to become disorientated without accurate navigation techniques.

As a submersible travels downwards, the pressure exerted on it by the water above also increases. At the depth of the Titanic wreck, the pressure is about 390 times greater than we experience on the surface.

Submersibles traveling to that depth need to be able to withstand these huge forces, and usually have thick metal hulls to do this.

• Read more about the treacherous waters around the Titanic wreck here

Rebecca Morelle
Science editor

We’ve been hearing from OceanGate co-founder Guillermo Sohnlein about the origins of the company.

At first the idea was to buy in a ready-made sub to head beneath the waves.

In 2009, the bought the Antipodes, a sub that could head about 300m deep - this made dives in in Puget Sound, Miami, San Francisco.

Then in 2013, the company bought a five-person sub that they called Cylcops I. This was a sub that could go deeper - to about 500m. It took passengers to the Andrea Doria wreck off Nantucket Island and to the Hudson Canyon.

After that, OceanGate decided to start designing their own sub - a prototype of Titan (which has also been called Cyclops II during the hearings).

The plan was for this to dive much deeper - to 4,000m down.

It was originally supposed to be made entirely of carbon fibre, but after a smaller model of the sub failed pressure tests, they switched to a version that would have titanium domes at either end.

But when they built this prototype, its hull failed.

So they took the parts from this and built a new hull, creating their final version of Titan that would head to the Titanic in 2021 and 2022 before it suffered a catastrophic failure in 2023.

Sohnlein tells the inquiry he left OceanGate at the end of January 2013.

"I didn't think it would make sense for me to stay," he says, noting his departure was a logistical choice.

But he notes his co-founder Stockton Rush wanted him to stay on and continue running the company, despite transferring the CEO title to Rush.

"Just in general I don't think it (made) sense," Sohnlein tells the committee.

It would have been much better for the company to hire engineers with the money that was paying my salary, he says.

The US Coast Guard has already heard a week's worth of testimony from people close to the Titan submersible that imploded last June, killing all five aboard.

Here are the five key takeaways from last week's testimony:

1. Crew's final words: 'All good here'

Investigators with the US Coast Guard revealed one of the crew's final messages before it lost contact with a ship above water: "All good here."

The hearing revealed other text messages between Titan and its mother ship as the deep-sea vessel began its trek to the sea floor to see the iconic British ocean liner that sank in 1912.

About one hour into the dive, the Titan sent a final message at a depth of 3,346m.

2. Witness recalls last look at Titan crew: 'Five people smiling'

Mission specialist Renata Rojas, who helped with the doomed trip as a volunteer, testified before the US Coast Guard on her interaction with the crew before the sub descended.

At one point, Rojas teared up while remembering "five people smiling" before boarding the Titan and heading below the water.

"They were just happy to go, that’s the memory I have," she said.

3. Whistleblower: Tragedy was 'inevitable'

OceanGate's former operations director David Lochridge testified to US Coast Guard investigators that he warned of potential safety issues before he was fired in 2018.

He claimed he was ignored.

Lochridge said he believed the deadly incident with the Titan was "inevitable" as the company "bypassed" standard rules.

4. New footage reveals Titan wreckage

The US Coast Guard released new footage showing the wreckage of the Titan sub on the bottom of the sea floor.

The deep-sea vessel is seen with the "OceanGate" logo on its side as debris is scattered around it.

5. Leading submersible manufacturer: Titan was 'not ready for primetime'

Patrick Lahey, the co-founder and chief executive of leading submersible manufacturer Triton, told investigators he wasn't impressed by the Titan submersible.

He toured the Titan sub that later imploded while on vacation in the Bahamas and said he "wasn't particularly impressed" by what he saw.

"It looked to me like a lot of the stuff was not quite ready for primetime," he added, saying he expressed his concerns to OceanGate.

Image source, US Coast Guard

Sohnlein tells the committee the original plan was for his co-founder and CEO Stockton Rush to "put in the money" and for Sohnlein to run the business of OceanGate.

When they started out, the two had "no intention of creating our own subs", Sohnlein said.

"We wanted to purchase a sub and learn more about them and learn what capabilities we needed our own sub to have," he said.

Investigators ask Sohnlein what the original vision for OceanGate was.

He says the vision was to create a fleet of deep-diving submersibles capable of carrying five people available for charter anywhere in the world.

That's exactly what the Titan sub was doing when it imploded in June 2023.

Rebecca Morelle
Science editor

The US Coast Guard has released a new image of the Titan sub, external showing how the dome fell off after a dive in 2021.

The dome came away after it was dropped while being lifted onto the deck from the water after a dive.

Fred Hagen, a paying passenger who made several dives on Titan was on that dive, described that incident to the US Coast Guard on Friday.

He said: "The force of the platform hitting the deck... it basically sheared off several bolts and they shot off like bullets. And the titanium dome fell off," he said.

He was also asked about other problems during dives he had made and he listed a litany of incidents.

On another dive, because the sub was incorrectly weighted, it was off balance and spiralled thousands of metres to the sea floor. Then when it got there the thrusters failed to work.

"The starboard thruster failed and we realized that all we could do was spin around in circles," he told the hearing.

On that same dive, some of the weights that were supposed to drop so the sub could ascend were stuck - but the Titan did eventually make its way back to the surface.

He also described how the sub briefly became caught in the wreckage of the Titanic and described a loud bang that was heard on another ascent.

However, he told the hearing he knew the sub was experimental and risky.

"It was clear that it was dangerous... It's kind of like jumping out of an airplane. I mean, you don't do it because it's safe. You do it because it's an adrenaline rush."

It was one of 118 technical incidents listed by the US Coast Guard with dives that took place in 2022 and 2023.

Image source, US Coast Guard

OceanGate co-founder Guillermo Sohnlein has begun testifying to the Coast Guard hearing.

He is the first witness during the second week of public hearings on the 2023 Titan sub disaster.

As a reminder, you can watch his testimony live at the top of this page, and we'll bring you text updates of the key lines.

Rebecca Morelle
Science editor

A transcript from a key Oceangate meeting held in 2018 has revealed the company’s CEO Stockton Rush saying that “no-one is dying under my watch - period.”

It captures a heated discussion between David Lochridge - OceanGate’s former director of marine operations - and Stockton Rush, plus three other Oceangate staff members.

The transcript was uploaded to the investigation website on Friday but sections of the document were redacted. The US Coast Guard has now confirmed to BBC News who was speaking during a key exchange.

David Lochridge was called to the meeting after compiling a “quality inspection report”, which raised multiple problems with the sub’s design.

In the transcript, Lochridge says: “I am addressing what I view as safety concerns, concerns I have mentioned verbally... which have been dismissed by everybody.”

Stockton Rush replies “I've listened to them and I have given you my response to them and you think my response is inadequate.”

Rush then goes on to say: “Everything I've done on this project is people telling me it won't work - you can't do that.”

He continues: “I have no desire to die. I've got a nice granddaughter. I am going to be around. I understand this kind of risk, and I'm going into it with eyes open and I think this is one of the safest things I will ever do.”

Later he says: “I can come up with 50 reasons why we have to call it off and we fail as a company. I'm not dying. No one is dying under my watch period.”

David Lochridge was fired after the meeting.

Caitlin Wilson
Live editor

Welcome to our live coverage of the second week of public hearings into the 2023 Titan sub disaster.

We are expecting to hear today from Guillermo Sohnlein, who co-founded OceanGate in 2009 with the company's late CEO Stockton Rush.

Investigators will also hear from Phil Brooks, OceanGate's former director of engineering, and Roy Thomas from the American Bureau of Shipping.

The second week of hearings comes after evidence released last week includes a transcript from a key meeting at the firm revealing Rush said in 2018: “No-one is dying under my watch - period.”

The inquiry heard last week from a former OceanGate employee and whistleblower David Lochridge, who had been considered about the Titan's safety before his firing in 2018.

The hearing also heard from industry expert Patrick Lahey, the chief executive of Triton submersibles - a leading manufacturer of deep sea crafts - who said he also had serious concerns about the Titan.

You can catch up on all the updates from last week here: Key takeaways from first week of Titan sub hearings.

Stick with us as we bring you all the latest from today's witnesses. You can watch the hearing live at the top of this page.