Zurich police say they have arrested a man in connection with the murder of an air traffic controller who was on duty at the time of a fatal crash.
Seventy-one people, mostly Russian school children, died when two planes crashed in Swiss-controlled airspace in July 2002.
The authorities are investigating a possible link between the 2002 crash and Tuesday evening's stabbing near Zurich.
Police said they arrested the suspect close to the town of Kloten where the murder took place.
The 36-year-old air traffic controller was stabbed at his home after an exchange of words with an unidentified man.
Police said on Wednesday that the killer was aged between 50 and 55, spoke broken German and may have been from eastern Europe.
The victim, who has not been named, died at the scene after his attacker escaped on foot.
The Danish victim worked for the Swiss air traffic control agency, Skyguide. He had lived in Switzerland for seven years and was the father of three children.
Skyguide said on Thursday that the operation of air traffic control in Zurich was back to normal.
Flights over the Zurich area were scaled back by 40 per cent on Wednesday out of consideration for staff and to ensure security.
Take-offs and landings at Zurich airport were also affected, leading to delays of up to 45 minutes.
“The swift lifting of the reduction was possible after intensive discussions with the controllers associations and thanks to rapid deployment of the Skyguide care team,” said the agency in a statement.
A Bashkirian Airlines plane carrying a large number of Russian schoolchildren collided with a DHL cargo plane over Überlingen in southern Germany on July 1, 2002.
Swiss air traffic control gave confusing instructions to the Russian pilot, which contributed to the crash.
The Russian pilot followed the controller’s instructions to descend, despite onboard equipment telling him to climb, leading the aircraft to collide with the cargo plane, which was also descending.
A lawyer representing the parents of the dead said on Wednesday that his clients were distressed by news of a possible connection between the crash and the murder.
"We reject any violent act... The families do not want to be associated with this," said Gerrit Wilmans.
Network errors blamed
Two weeks after the tragedy, the unidentified controller admitted in a statement that network errors had been to blame.
The Federal Office for Civil Aviation moved him to other duties after a period of psychological treatment.
Skyguide later came under heavy criticism when it emerged that only one person was on duty during the night of the crash.
Late last year, the first compensation payouts reached a number of victims’ families after Skyguide negotiated an out-of-court settlement with some relatives.
Talks are continuing with the relatives of other victims over compensation packages.
The German authorities are still investigating the Überlingen tragedy; their report is expected later this year.
swissinfo with agencies
Police have arrested a suspect in connection with Tuesday's murder of an air traffic controller.
The unnamed victim was on duty the night of a midair collision between a Russian jet and a cargo plane, which killed 71 people in July 2002.
His confusing advice is thought to have caused the crash.
Police are not ruling out a link between the two incidents.
July 1, 2002: Bashkirian Airlines jet and DHL cargo plane collide in Swiss airspace, killing 71.
July 13, 2002: the air traffic controller on duty admits network errors were to blame.
June 2003: Switzerland, Germany and Skyguide agree to set up a compensation fund.
November 2003: a first round of compensation reaches the families of 12 Russian victims.
February 24, 2004: the air traffic controller on duty at the time of the crash is stabbed to death.
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