The families who believe their relatives survived the 2018 sinking of an Iranian oil tanker in the East China Sea may soon have some evidence put on the record in US federal court.

US District Judge Amy Berman Jackson ruled on Tuesday that the families' lawyers can now press ahead with limited fact discovery in a US federal court lawsuit against National Iranian Tanker Co (NITC).

In the case, lawyers for the plaintiffs argue that at least 10 of the 164,000-dwt Sanchi's (built 2008) crew are still alive after the ship crashed and sank.

Fuelling the families' belief are more than 1,000 inexplicable phone calls, received at all hours from various international numbers, suspected of being from their ostensibly dead relatives.

"Defendants have denied the families access to information about the incident and their relatives," attorney Ali Herischi wrote in a motion for discovery.

"In the official crash report approved by Iran, China, Panama and Hong Kong, officials state that the majority of the crew are considered 'missing' and that only three bodies were discovered in the aftermath."

Herischi, whose Herischi & Associates is based in Maryland, had initially moved for limited and expedited fact discovery.

But Berman Jackson declined to allow discovery to move faster. She said the lawsuit's third parties were not being obstructive.

Politicians named

In addition to NITC, the lawsuit names politicians Ali Rabiei and Alaeddin Boroujerdi as defendants.

None responded to the lawsuit, filed in December in the federal court in Washington, DC, and all three were ruled to be in default.

When the lawsuit was filed, NITC said it had been made aware of the lawsuit through media channels.

The Sanchi crashed after it collided with the 76,000-dwt CF Crystal (built 2011), causing an oil spill.

For a week, search parties looked for the Sanchi's crew, to no avail, while the CF Crystal's seafarers were saved.

In addition to the phone calls and the crash reports, the families say the Iranian government refused to look into the crash at the national prosecutor's behest and that NITC offered to hire one member of each family if they agreed their relatives were dead.

Herischi — a regular litigant on behalf of Iranian defendants and against the Iranian government — told TradeWinds after the lawsuit was filed that his goal was to get the case into discovery to try to get the families closure.

He was not focused on finding out why.

"Was it insurance fraud? Was it an intentional accident? Was it domestic politics? Was it international politics? I don't know," he said at the time.

"I try not to focus my case on the theory. We are trying to get to the fact."