Jaroslaw Kaczynski - twin brother of the late president who died in the Smolensk air crash - gave evidence for three hours, Tuesday, at the Military District Prosecutor's Office in Warsaw as part of the investigation into the causes of the April 10 tragedy.

Kaczynski - who was a losing candidate in the recent presidential elections - was tight-lipped about what questions he was asked and what his answers were when he emerged from the session at lunchtime.

"It was a hearing - what could be expected," he told journalists, adding that "nothing during the hearing was difficult nor unusual". He then refused to comment further.

Meanwhile, Poland’s attorney general, Andrzej Seremet, said progress had been made in the examination of the plane’s black boxes.

“Polish experts investigating the recordings of the black boxes recorders of the TU 154, which crashed near Smolensk on April 10, have managed to decipher several words [by either pilots or air traffic control] which may be of key importance to the investigation”, he said.

He added that he will suggest that investigative officers dealing with the case reveal the whole material to the public in due course.

At a press conference in Warsaw this afternoon, the Attorney General said he was “slightly’ concerned with the lack of response on part of the Russian side concerning an agreement to pass all relevant documents over to Polish investigators. Poland expects Russia to provide a further 10 volumes of documents in August. “Such a promise was made,” Seremet said, adding that the general military prosecutor will be leaving for Moscow in mid August.

Andrzej Seremet admitted that Polish prosecutors have not been present during the autopsies of the bodies of the victims of the crash - an issue which has upset many of the families who lost loved ones in the crash. The only exception was the autopsy of the late president, Lech Kaczynski’s body.

He explained that Polish prosecutors arrived in Smolensk after all post mortem examinations were completed and pointed out that this was not an extraordinary situation. A similar case was when a Polish coach crashed in France in July 2007, killing 26.

Commenting on accusations that the burial of most of the 96 victims was conducted without any forensic examinations in Poland, Andrzej Seremet explained that the consent for burial does not lie in the hands of the prosecution.

Poland’s Attorney General announced that press conferences by the military prosecution concerning the Smolensk air crash will be held every two weeks.

On Wednesday Seremet is to meet with the families of the Smolensk victims, to present results of the investigation so far and explian the rights to which the families are entitled.

Seremet expressed the hope that the meeting will help in clarifying the misunderstandings which have arisen between the prosecution and the families.

The Prosecutor general said that during the investigation into the Smolensk crash, in which died 96 people , 40 volumes have already been collected and 204 witnesses interrogated. Another 100 is planned for questioning concerning the organization of the flight of the presidential plane. (ab/pg)