A Polish plane crashed on its way to the site of a Soviet massacre of Polish officers during World War II on Saturday, killing everyone on board, including the president and many others of Poland's top political and military leaders. Days before the crash Prime Minister Vladimir Putin became the first Russian leader to join Polish officials in commemorating the 1940 massacre at Katyn in western Russia.

Poland has been waiting for a Russian apology for more than half century. State apologies are difficult when it relates to a historical event, such as the Katyn massacre. Some people question whether successors should be responsible for their predecessors' actions. Jennifer Lind, an assistant professor of government at Dartmouth University, developed an "apology theory," which posits that the way a state remembers its past shapes how others perceive its intentions. States that glorify or deny past violence appear to have hostile intentions and thus more threatening; states that admit and atone for past violence appear benign.

For example, the Japanese have yet to shoulder the obligation left by their forerunners who offended their Asian neighbors. We can easily sense the threat from Japan. On the other hand, German contrition for Nazi crimes has successfully reduced others' threat perception of it.

Relations between Poland and Russia have long been tense, which can be partly attributed to Moscow's denial about its involvement in the Katyn killings. Poland could feel Russia's intimidation. It joined the European Union in 2004 and turned to NATO for help. President Lech Kaczynski told the New York Times, "It was obvious to us that this was the only tough security structure there was in the world and that the membership of NATO would only mean benefits for Poland." He then made efforts to enlarge the organization by courting Ukraine and Georgia, believing that a strong NATO would prevent Russia from swaying Eastern Europe.

It is clear what Russia needs to do to reduce tensions with its neighbors. Putin has taken a major step to ameliorate relations by observing the massacre's anniversary. The plane crash may remind us that there has still been no official apology, but it should not be the impetus for one, either. A Russian apology should be for Katyn, and Katyn alone.

The author is a researcher with the Institute of Journalism and Communication, Chinese Academy of Social Sciences.