Comprehensive post-mortem examinations are "the key to reconstructing the chain of events and establishing the cause of the crash, despite the several years which have passed," the state prosecution said in a statement.

Six of the previously exhumed nine bodies were reportedly wrongly identified, the prosecution added, and re-opening the coffins - which were sealed in Russia - was necessary to confirm all identities, it said.

Lech Kaczynski, the then president and twin brother of Poland's most powerful current politician, Jaroslaw Kaczynski, was killed in the crash in April 2010, as were the first lady, army commanders, the central bank head and other top state officials among a total of 96 dead.

Old scores to settle

An inquiry that was set up by the previous centrist government of Civic platform (PO) - then headed by the current European Council president Donald Tusk - returned a verdict of pilot error.

The plane had crashed in dense fog on approach to Smolensk airport, and separate commissions of aviation experts in Poland and Russia put the blame on insufficient crew training and human error in adverse circumstances.

Jaroslaw Kaczynski - a bitter enemy of Tusk - seems intent on finding and punishing those guilty of his brother's death. The Law and Justice (PiS) party leader says the crash may have been caused by an explosion on board, repeatedly pointing the finger at Tusk, who he says caused the crash through negligence.

Defense Minister Antoni Macierewicz (pictured left) said on Tuesday in Warsaw that the plane had "disintegrated" meters above the ground.

PiS has never accused Russia of orchestrating the president's death but has repeatedly said the Kremlin benefited from the crash, and PiS officials have accused Moscow of prolonging its investigation and withholding evidence, such as the black boxes and the plane's wreckage. Russia rejects the claims.

The politics of death

The move comes only a few months after the new government merged the posts of prosecutor-general and justice minister, thus giving itself more direct control over the investigation. It also comes on the back of a decision by the PiS government to relaunch an investigation into the case.

The crash took place near Smolensk, in western Russia, in an area imbued with historical prescience due to the murder of 22,000 Polish officers and intellectuals by Soviet secret police forces in 1940, a crime that was blamed on Nazi Germany for several decades until the end of communism in Russia.

"I hope there will be more court verdicts in the case," Kaczynski said after the verdict. The PiS government has been widely critisized since coming to power in late 2015 not only for politicizing the judiciary, the civil service, public media and state-owned firms, but also for opening up old fights with political opponents, including former President Lech Walesa.

A first victim

Meanwhile, a court on Tuesday handed down a suspended prison term to a former deputy head of government security over the crash. The Warsaw Provincial Court's decision is the first conviction connected to the crash.

General Pawel Bielawny was found guilty of "knowingly neglecting his duties and exposing Kaczynski to danger by failing to order a proper inspection of Smolensk airport and failing to send experienced officers to await the plane's landing."

The court said it was a mistake of the organizers to have chosen an almost unused airport as a landing place for top state officials.

Bielawny, a former deputy head of the Government Protection Bureau (BOR), was given an 18-month suspended sentence and a 10,000-zloty (2,270-euro) fine.

The verdict is subject to appeal.

jbh/kms (Reuters, AP, dpa)