Polish authorities have questioned Donald Tusk, the president of the European Council, as a witness in an investigation into the 2010 jet crash in Russia that killed Poland's then-president Lech Kaczynski and 95 others.
Tusk, who was the Polish prime minister at the time, told reporters after the more-than-eight-hour interrogation that he would not be intimidated by the proceedings, which his lawyer described as politically motivated.
Jaroslaw Kaczynski, the country's ruling party leader and the brother of the former president, said Tusk "should be afraid.''
But Tusk said, "I do not have anything to fear. And Mr. Kaczynski will not scare me, no matter how badly he wants to get me."
Kaczynski has long insisted that the crash was no accident and that Tusk was morally responsible for the death of his twin brother.
Polish and Russian investigators determined at the time that pilot error, bad weather and poor air-traffic control were to blame for the crash.
Prosecutors have said they are trying to determine why Polish authorities at the time did not take part in the autopsies, which were performed by Russians and later shown to be sloppy. Exhumations have revealed that some body parts got mixed up and were buried in the wrong graves.
Tusk's Polish supporters see the questioning as part of a bitter feud going back years that pits him against Kaczynski, the man who directs most government decisions now.
One of the EU's top leaders since 2014, Tusk is considered one of the most charismatic and effective politicians that Poland has had in many years, and the only one able to unite a weak and divided political opposition. Should he ever return to Polish politics, he would represent a major threat to Kaczynski.