The air traffic controller on duty when two planes collided over southern Germany in July 2002 has been killed at his home in Zurich.
Police are looking for a man, speaking broken German, who fled on foot after stabbing the controller in front of his wife after a brief exchange of words.
They said they could not rule out a link between the killing and the crash.
Seventy-one people - mostly Russian schoolchildren - died in the disaster. The controller was not publicly named.
Swiss police said a link to the crash was a "central issue" in their hunt for the attacker, who is described as being powerfully built and aged around 50.
"(Revenge) cannot be ruled out," public prosecutor Pascal Gossner told Reuters news agency. "We are looking into whether there is a link between the killing and the air accident."
But added: "We will also be looking into the personal circumstances of the victim".
The prosecutor said it was "speculation" that the murder was an act of vengeance on behalf of the bereaved families. "You have to say he spoke broken German. But you cannot say he was from Russia."
A lawyer for families of the crash victims said they were distressed at such a connection being made.
"We reject any violent act... The families do not want to be associated with this," Gerrit Wilmans told Reuters.
The dead man's employer, the Swiss air traffic agency Skyguide, said it was appalled by Tuesday's killing and that its employees were "in shock".
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