Shell’s US law firm is refusing to hand over more than 100,000 internal documents crucial to a legal case in the Netherlands which is alleging the oil giant’s complicity in the unlawful arrest, detention, and execution of nine men in Nigeria in the 1990s, Amnesty International said ahead of a US Court of Appeals hearing next week.

The execution of the “Ogoni Nine”, including the renowned writer Ken Saro-Wiwa, by the Nigerian state in 1995 sparked global outrage. It was the culmination of a brutal campaign by Nigeria’s military government to silence protests in the oil-producing Niger Delta region.

Others executed along with Saro-Wiwa were, Saturday Dobee, Nordu Eawo, Daniel Gbooko, Paul Levera, Felix Nuate, Baribor Bera, Barinem Kiobel, and John Kpuine.

After a 20-year battle for justice, on June 28 four of the men’s widows, led by Esther Kiobel, filed a legal writ against Shell in the Netherlands. Shell is trying to prevent the release of information vital to the case.

Meanwhile, it has been revealed by rights organisation, Amnesty International that Shell may be withholding the information because it has skeletons in its cupboard.

After reviewing the available evidence, the rights organisation held that Shell, during the period in reference, encouraged the authorities in their campaign to stop the protests, even after they knew human rights violations had occurred.

Amnesty International said it has presented the allegations to Shell, but the oil company denied the allegation, saying it “did not collude with the military authorities to suppress community unrest and in no way encouraged or advocated any act of violence in Nigeria.”

On September 12 the Second Circuit Court of Appeals in New York will hear the first appeal by Shell’s lawyers Cravath, Swaine & Moore, LLP against a federal court order to turn over the documents.

“Shell has gone to extraordinary lengths to withhold this critical information. Because the documents in question are so old, it is highly unlikely that there are legitimate business reasons for keeping them confidential. So what does Shell have to hide?” said Audrey Gaughran, Senior Director of Research at Amnesty International.

“Having reviewed the available evidence, Amnesty International believes that Shell was complicit in putting the Ogoni Nine at the mercy of a government it knew to be serial human rights abuser. Given the seriousness of the allegations, it is vital that Shell releases the rest of the information. It cannot be allowed to hide behind expensive legal teams and sleights of hand to avoid facing justice.”

Esther Kiobel who first filed a lawsuit against Shell in 2001 is represented in the proceedings by EarthRights International, an international human right, and environmental justice NGO.

After more than 10 years since the suit was first filed, the US Supreme Court in 2013, ruled that the US did not have jurisdiction, without hearing the substance of the case.

Shell was represented by Cravath, which still holds more than 100,000 confidential Shell documents produced through discovery in the original case.

On January 24, 2017, a New York district court ordered Shell to turn over the documents.