The Russian government's actions raise too many questions about the April 10 airplane crash that killed many of the most anti-Russian leaders of Poland. My recent conversations with informed Polish sources reveal so many irregularities with how the Russian government handled the crash that nobody should presume that the disaster was accidental until all the facts are in.

I knew four of the Polish officials who died in the crash and have a special interest in raising unpleasant questions and pushing for full answers. Here are the issues that surfaced in my recent discussions one month after the disaster that killed Polish President Lech Kaczynski and other senior Polish figures:

President Kaczynski and his entourage were traveling to Smolensk, Russia, near the Katyn forest where the Soviet NKVD (Chekists) murdered thousands of Polish officers during World War II. Kaczynski was a strong critic of Moscow and its failure to repudiate its Soviet past. His rival, Prime Minister Donald Tusk, has taken a much softer approach toward Moscow. Tusk was not on the plane.

Tusk held an official observance of the anniversary of the Katyn massacre with Russian Prime Minister Vladimir Putin. Tusk and Putin agreed in advance that Kaczynski would not be part of the official commemoration, and that Kaczynski would arrive separately on a "private" visit.

In the hour or so after the crash, the Russian government officially blamed the disaster on "pilot error," before an investigation had begun. Russian officials said the Polish pilot did not speak Russian, when the pilot spoke excellent Russian.

Putin has assumed personal control of the crash investigation.

The Russian government has maintained total, opaque control of the crash investigation, in violation of the Chicago Convention that governs international air crashes and in violation of a bilateral 1993 agreement that joint commissions would conduct investigations of aircraft disasters affecting both countries.

All 97 bodies of the crash victims, including the late Polish president, were removed from the crash site before Polish authorities could arrive, and brought to Poland.

No independent autopsies of the crash victims was permitted, and Polish officials did not have the ability to be present during the autopsies.

All personal effects of the crash victims were removed from the scene and taken to Moscow before any Polish official could arrive.

Russian security officers interrogated Polish family members who traveled to Moscow to recover the bodies - sometimes for hours - and were denied access to the bodies until the interrogations were complete. The daughter of parliament member Zbigniew Wasserman, who oversaw the security services, went to Russia for her father's body but was detained six hours and interrogated. She was repeatedly denied the right to have a Polish official present for her interrogation.

Russian officials required Polish family members of the victims to sign that they were satisfied that the personal effects were all in order or had been destroyed in the crash; those who did not want to sign were told that they would not have access to their loved ones' remains until they did sign.

There has been no independent verification that all the bodies are accounted for. The bodies were returned to Poland in sealed coffins for burial. Families of the victims were not permitted to open the coffins. Under Polish law, official permission from the state prosecutor's office is required to exhume a body, and that office has denied family requests, apparently for fear of offending the Russian government.

The Russian government has not turned over two of the plane's black boxes to Polish authorities, despite repeated formal Polish requests. Two of the three boxes aboard the Russian-made Tupolev 154 presidential plane were of Russian manufacture, and one was Polish. The Russian government briefly gave the Polish-made black box to the Polish government, then took it back. Russia has refused to hand over the two Russian-made black boxes.

Russia's intelligence services have used the disaster as a spy operation against Poland and the NATO alliance. Russian authorities recovered laptop computers, flash drives, cell phones and other electronic gear belonging to the Polish president, senior military leaders, security chief and other top officials who died on the flight. Those items contained sensitive names, telephone numbers, correspondents, documents, and top secret military and diplomatic codes. The Russians delayed for days and sometimes weeks before returning the items. Some of the items, such as flash drives belonging to officials with responsibility for security and intelligence matters, are missing.

Russian officials waited six days before returning President Kaczynski's Nokia cell phone to the Polish government.

After Russian security officers removed what they wanted from the site, they left the site unguarded. Polish journalists discovered that the site was unattended.

A Polish aviation official who serves as a day-to-day interlocutor with the Russians on the matter told a Polish parliamentary commission, "We know everything that happened but the Russians forbid us to tell you." The official said that it could take as long as a year before Russia releases the information.

Most Polish officials seem to believe that the Russian government played some role in the crash. Kaczynski was the most anti-Russian leader in Europe, and his entourage on the plane included similarly minded senior military and security officials. Kaczynski's twin brother, Jaroslaw, was supposed to have been on the plane as well. On the heels of years of Russian assassinations of Putin's internal opponents, the assassination by radioactive polonium of a top KGB defector in London, the attempted assassination of the anti-Russian leader of Ukraine, the Moscow-backed overthrow of the government of Kyrgyzstan and other actions, Polish officials can only presume that Putin may have had a hand in the April 10 crash. The disaster took place on Russian soil, with Putin's secret services in total control of the probe that he personally directs.

Polish Prime Minister Donald Tusk, who opposed the late president and is in charge of day-to-day affairs of state, appears fearful of Russia and does not want to say or do anything to upset Putin.

Tusk says that those who suspect foul play are motivated by "anti-Russian" prejudice, but sources close to him say he has never definitively called the crash an "accident."

"Prime Minister Tusk, at every moment from the crash, says, 'We will do this or that because the Russian government wants it and we don't want to offend the Russians.' Tusk acts like he is in fear," a source close to Tusk tells me.

Why has Prime Minister Tusk acted like in such a servile manner toward Moscow in the wake of the April 10 crash? If the crash was an accident, what is Tusk afraid of?