Jarosław Kaczyński, leader of the Law and Justice party and erstwhile presidential candidate, took the stand on Tuesday before the Regional Prosecutor's Office in Warsaw as a witness in a hearing about the Smolensk tragedy.

The prosecution is investigating the circumstances surrounding the April 10 plane crash which took 96 lives, including that of President Lech Kaczyński, Jarosław's twin.

“It was what you could expect of a hearing,” Mr Kaczyński said after leaving the prosecutor's office.

“The interrogation was comprehensive. It proceeded in a friendly atmosphere ... there was full freedom of speech,” Mr Kaczynski's representative Piotr Pszczółkowski said after the trial. “This hearing will dispel some doubts,” he added. However, Mr Pszczółkowski did not reveal any details.

Prior to the trial experts said that the last telephone conversation Mr Kaczyński had with his twin before the latter died in the tragedy would be significant to the investigation.Of particular interest to Smolensk investigators could have been a telephone conversation which Mr Kaczyński had with his twin before the latter died in the tragedy.

Piotr Schramm, who is representing some of the families of the Smolensk disaster, told TVN24 that if the conversation had been held shortly before the crash, Mr Kaczyński could have picked up clues about what was happening from the tone of the president's voice.

“Maybe even direct information about what the communications with the Russians were like, what the weather was like at the airport,” he said.

Some have questioned whether Mr Kaczyński can be trusted to reveal everything he knows. Should he have been told of any pressure the president had put on pilots to land, it would be difficult for Mr Kaczyński to reveal that before the prosecutor, Mr Schramm said.

However, Rafał Rogalski, Mr Kaczyński's plenipotentiary, said he knew what was said during the conversation and doubted that it would be of any help in the investigation.

Mr Kaczyński will later be questioned by Russian investigators.