Polish Defense Minister Antoni Macierewicz arrives at a press conference in Warsaw on Sept. 15, 2016, given by the commission investigating the 2010 presidential plane crash. (Wojtek Radwanski/AFP/Getty Images)

Poland's investigation into the 2010 plane crash in Russia that killed President Lech Kaczynski was thrust back into the spotlight Thursday, as a government commission asserted that flight recordings were manipulated in possible attempts to mask the cause of the tragedy.

Kaczynski’s twin brother, Jaroslaw Kaczynski, 67, is now the leader of Poland’s governing Law and Justice party and has dressed in black since his brother’s death. Critics say the new inquiry is motivated by his desire for revenge and belief in a vast conspiracy that led to his brother's death.

An investigation under the previous government found that the crash was caused by pilot error in heavy fog at Smolensk airport, where the Polish delegation was traveling for a joint memorial with Russia marking the massacre of Polish officers by Soviet agents during World War II.

Reports on leaked transcripts from recording devices in the cockpit indicated that Kaczynski's entourage had pressured the pilots to land despite the poor conditions.

The crash of the Tupolev aircraft, operated by the Polish air force, killed all 96 people on board, including Kaczynski’s wife, Maria Kaczynska, and many senior military and political figures.

On Thursday, a new Polish commission to review the crash said that “black box” recordings recovered from the accident had been “manipulated and shortened,” with several seconds of audio missing.

Polish Defense Minister Antoni Macierewicz said there was “irrefutable proof of falsifications, manipulations and obfuscation of the truth.”

Poland's government is expending tremendous effort in a painful reexamination of the crash. Investigators earlier this week confirmed that they would exhume the bodies of most of the victims, including Kaczynski and his wife, to search for clues to foul play.

“Comprehensive post-mortem examinations . . . will be important for determining the injuries of the victims and the causes of their deaths, as well as reconstructing the final moments of the disaster and its causes,” Poland’s national prosecutor said in June.

The commission, formed in March, is not tasked with naming alleged culprits, Macierewicz said. But he has indirectly accused Russia of sabotaging the plane, and former prime minister Donald Tusk, now president of the European Council, has been accused by political opponents of intentionally botching the initial investigation.

Five Polish officials, including a former aide to Tusk, are on trial for alleged negligence in planning the flight.

In 2012, Jaroslaw Kaczynski told Tusk in parliament that he bore “100 percent of the responsibility for the catastrophe.”

Russian Foreign Ministry spokeswoman Maria Zakharova on Thursday called accusations against Russia “irresponsible and provocative” and said the Polish side should produce evidence before engaging in speculation.

“These are very serious things,” she said.

The accusations of a vast government coverup and rogue Russian air-traffic controllers read like a thriller.

And, in fact, top Polish officials last week attended the premiere of a blockbuster film called Smolensk, which follows a crusading Polish reporter debunking official explanations for the accident. The plot points to sabotage.

“Before we were forbidden to ask who was behind the [World War II] murders” by the Soviets, one of the characters says in a publicity clip for the movie. "Today we are afraid to ask what really happened in Smolensk."

The film’s director, Antoni Krauze, called the movie a “protest against the manipulations with the truth.”

President Andrzej Duda, a former member of Kaczynski’s party, and Prime Minister Beata Szydlo attended the premiere at Warsaw’s National Opera House, along with family members of the crash victims, including Kaczynski.