Technical experts have begun examining the debris of Poland's presidential plane to determine what caused its deadly crash.

Ninety-six people, including Polish President Lech Kaczynski, his wife and many top state and military leaders, died when the plane went down in dense fog in Smolensk, Russia, on April 10.

Russian and Polish forensic experts working in Moscow still need to identify 20 of the victims, including the members of the cabin crew, using DNA tests, said military prosecutor spokesman Col. Zbigniew Rzepa.

Experts laid out the debris, reconstructing the plane's shape, on the grounds of Smolensk airport on Monday.

Some of the findings, along with transcripts of the cockpit conversations, are to be released later this week when Poland's chief military prosecutor, Krzysztof Parulski, returns to Poland.

So far investigators have tipped human error as the likely cause.

Kaczynski and his wife, Maria, were buried Sunday after an elaborate state funeral.

Burials of the victims continued Monday. One of them was a state ceremony at Warsaw's Gothic St. John's Cathedral for Ryszard Kaczorowski, aged 90, who from 1989-90 was the last president of Poland's government-in-exile that found refuge in London.