The remains of the late Polish President Lech Kaczynski and his wife Maria have been exhumed as part of a new investigation into the fatal plane crash in Smolensk six years ago.
The crash killed the couple and all 94 others on board.
The remains were removed from a marble sarcophagus in the crypt of Krakow's historic Wawel Cathedral.
Prosecutors say fresh examinations are necessary to ensure the victims were correctly identified.
They say the original autopsies carried out in Russia contained irregularities.
Indeed, several exhumations carried out four years ago found that some of the victims were buried in the wrong graves.
But more than that, prosecutors say the forensic tests may just provide new evidence about the cause of the disaster.
Further exhumations will be carried out in stages over the next 12 months.
The decision is highly controversial because it is opposed by some of the families of the victims and is being carried out without their consent.
Some families agree with the procedure, but 17 families appealed to church and political leaders to prevent what they called a "ruthless" and "cruel" decision.
In an opinion poll last month, just 10% of respondents supported the exhumations.
President Kaczynski's plane crashed in dense fog just short of the runway of a former military airbase in the Russian city of Smolensk on 10 April 2010.
Senior state and military officials had been on their way to a ceremony to mark the 70th anniversary of the Katyn massacre in which more than 20,000 Polish officers were murdered by the Soviet secret police.
Russian and Polish investigations concluded the crash was mainly caused by pilot error.
Both reports said the pilots warned officials that the weather conditions were not sufficient to attempt a landing but a decision was taken to descend to see if the runway could be sighted.
The pilots flew too fast and too low and ignored repeated electronic warnings to pull up before smashing into the ground.
The tragedy initially united the country in grief but it has subsequently caused much division.
The investigations' findings have never satisfied President Kaczynski's twin brother, Jaroslaw, who leads the governing Law and Justice party, which took office a year ago.
Mr Kaczynski's close ally, defence minister Antoni Macierewicz, has launched a fresh investigation.
He has previously spoken about two explosions moments before the plane crashed and the examinations will check for traces of explosives. Indeed, about one quarter of Poles believe that President Kaczynski was assassinated.
While more than two thirds of Poles do not believe the crash has been fully explained, a majority believe the crash was an accident. Previous probes explicitly ruled out an explosion.
Mr Macierewicz has been investigating the crash circumstances for more than five years now - he led an earlier parliamentary probe whilst in opposition - but he has yet to publish any new evidence disproving the previous findings.