UNITED NATIONS (AP) — A former judge who reviewed new information on the mysterious 1961 plane crash that killed U.N. Secretary-General Dag Hammarskjold says "it is plausible that an external attack or threat may have been a cause of the crash."

Tanzania's former chief justice Mohamed Chande Othman said in a report released Wednesday that the chartered DC-6 plane registered as flight SE-BDY could have crashed as a result of a direct attack or a momentary distraction of the pilots at a crucial moment in their descent.

"There is a significant amount of evidence from eyewitnesses that they observed more than one aircraft in the air, that the other aircraft may have been a jet, that SE-BDY was on fire before it crashed, and/or that SE-BDY was fired upon or otherwise actively engaged by another aircraft," Othman said.

"In its totality, this evidence is not easily dismissed," the recently retired judge said.

Othman said it also remains conceivable that the crash resulted from pilot error.

He said he also has been trying to get documents from South Africa on "Operation Celeste" which purportedly raise the possibility of a bomb being placed on SE-BDY to sabotage it and "remove" Hammarskjold.

Despite "the significant amount of new information," Othman said, further investigation is needed to finally establish the facts.

Widely considered the U.N.'s most effective chief, Hammarskjold, a Swedish diplomat, died when his plane crashed near Ndola Airport in modern-day Zambia, then the British protectorate of Northern Rhodesia.

He was on a peace mission, flying into a war zone infested with mercenaries and riven by Cold War tension. Congo won its freedom from Belgium in 1960, but foreign multinationals coveted its vast mineral wealth and the country was challenged by a Western-backed insurgency in Katanga province, which hosted mining interests belonging to the United States, Britain, and Belgium.

An independent panel reviewing new information about the crash said in July 2015 that the United States and Britain retained some classified files, and that South Africa had not responded to several requests for information.

The panel put to rest claims that Hammarskjold was assassinated after surviving the crash — a point echoed by Othman who said it is almost certain the U.N. chief and members of his party were not killed after landing, and that all passengers died from injuries during the crash, instantaneously or soon after.

It has long been rumored that Hammarskjold's plane was shot down, and the panel provided new information about a possible aerial attack or interference. In February, Secretary-General Antonio Guterres appointed Othman to review the new information.

Othman said in the report that he reviewed a "significant amount of new information," especially on probable intercepts of U.N. communications and the capacity of the armed forces of Katanga to have staged a possible attack on Hammarskjold's plane.

Othman said he sent requests for additional information to eight countries most likely to hold relevant new material — Belgium, Canada, France, Germany, Russia, South Africa, the United Kingdom and the United States — as well as the United Nations and some individuals. He received responses from Belgium, Canada, Germany, the United Kingdom and the United States.

The 2015 panel gave a "moderate" value to claims by two Americans — Charles Southall, a former U.S. Navy commander, and Paul Abram, a former U.S. Air Force Security Services officer — who either listened to or read a transcript of an intercept of radio transmissions the night of Sept. 17-18, 1961, which they believe was reporting an attack on Hammarskjold's plane that resulted in the crash.

Othman said Southall died in 2015 but it should be possible to conduct an inquiry into Abram's claim. He said the U.S. only confirmed Abram's service record in July, "along with new information that disputes Abram's location at the time he reported hearing the intercept."

Othman said he also received new information from the UK, U.S., U.N. and individuals "which appears to establish that Rhodesian and United Kingdom authorities intercepted United Nations communications in the Congo in 1961."

He said he also received confirmation from the U.S. that it had between one and three Dakota aircraft, which had sophisticated communications, in and around Ndola on the fatal night.

One theory about an external attack, Othman said, is that Hammarskjold's plane may have been "attacked, menaced or distracted by a Fouga Magister jet operated by Katangan forces."

He said this year the U.S. and other sources provided information appearing to substantiate that around Feb. 16, 1961, three Fouga jets purchased from France were delivered to Katanga by a U.S. commercial jet, "against objections of the government of the United States." Othman said he rated this new information "as being strong."

He said he has not been able to rule out that another non-Katangan aircraft was in the air the night of the crash.

Othman said he also received information "regarding an unauthenticated claim made by a Belgian pilot, 'Beukels', to Claude de Kemoularia in 1967 that Beukels shot down or otherwise forced SE-BDY to crash."

He said he was given access for the first time to de Kemoularia's agendas and many of his personal records, and reviewed his letters showing he had gone to French and Swedish authorities about Beukels' claim "much earlier than previously understood." But Othman said the identity of Beukels remains a mystery and more information is needed.

Secretary-General Gutteres announced Wednesday that he transmitted Othman's report to the U.N. General Assembly.

He called on the 193-member world body to endorse Othman's recommendations — especially his call on member states to appoint an independent high-ranking official to review intelligence, defense and security archives for information on what happened the night Hammarskjold's plane crashed.