Last year, five people hoping to view the Titanic wreckage died when their submersible imploded in the Atlantic Ocean. This week, a Coast Guard panel that's investigating the Titan disaster listened to four days of testimony that has raised serious questions about whether warning signs were ignored. The panel plans to listen to another five days of testimony next week.

Here's what witnesses have been saying so far:

The lead engineer says he wouldn't get in the Titan

When testifying about a dive that took place several years before the fatal accident, lead engineer Tony Nissen said he felt pressured to get the Titan ready and he refused to pilot it.

“I’m not getting in it," Nissen said he told Stockton Rush, the co-founder of OceanGate, the company that owned the Titan. Nissen said Rush was difficult to work for, made demands that often changed day-to-day, and was focused on costs and schedules. Nissen said he tried to keep his clashes with Rush hidden so others in the company wouldn't be aware of the friction.

The Titan malfunctioned a few days before its fatal dive

Scientific director Steven Ross said that on a dive just a few days before the Titan imploded, the vessel had a problem with its ballast, which keeps vessels stable. The issue caused passengers to “tumble about" and crash into the bulkhead, he said.

“One passenger was hanging upside down. The other two managed to wedge themselves into the bow,” Ross testified.

He said nobody was injured but it took an hour to get the vessel out of the water. He said he didn't know if a safety assessment or hull inspection was carried out after the incident.

It wasn't the first time the Titan had problems

A paid passenger on a 2021 mission to the Titanic said the journey was aborted when the vessel started experiencing mechanical problems.

“We realized that all it could do was spin around in circles, making right turns,” said Fred Hagen. “At this juncture, we obviously weren’t going to be able to navigate to the Titanic.”

He said the Titan resurfaced and the mission was scrapped. Hagen said he was aware of the risks involved in the dive.

“Anyone that wanted to go was either delusional if they didn’t think that it was dangerous, or they were embracing the risk,” he said.

One employee said authorities ignored his concerns

Operations director David Lochridge said the tragedy could possibly have been prevented if a federal agency had investigated the concerns he raised with them on multiple occasions.

Lochridge said that eight months after he filed a complaint with the Occupational Safety and Health Administration, a caseworker told him the agency had not begun investigating and there were still 11 cases ahead of his. By that time, OceanGate was suing Lochridge and he had filed a countersuit. A couple of months later, Lochridge said, he decided to walk away from the complaint. He said the case was closed and both lawsuits were dropped.