The Swiss air traffic control authority, Skyguide, has unveiled a memorial in Zurich to the victims of the 2002 Überlingen plane crash over southern Germany.
Seventy-one people died, 45 of them Russian children, when two jets collided over Swiss-controlled airspace. Two years later a distraught father murdered the air traffic controller on sole duty at the time.
The 2004 killing and compensation claims from families of the victims have ensured the disaster has not faded from the public memory.
A Skyguide spokesman said the memorial was intended as a way of remembering all the victims, including the murdered Skyguide controller.
Skyguide's director, Alain Rossier, representatives from the Russian embassy in Bern, families of the victims, local people from Überlingen and Skyguide staff were expected to attend the commemoration ceremony.
A 2m-high memorial sculpture made of glass and stone was unveiled in the main entrance of Skyguide's new headquarters in Dübendorf close to Zurich airport.
The sculpture features symbolic "wings" representing the 71 victims of the accident on July 1, 2002, and the controller killed on February 24, 2004; the two dates are engraved in gold on the memorial.
"It's not just a sculpture in an entrance hall – it's also a sign of rapprochement," Skyguide spokesman Patrick Herr told swissinfo.
The remembrance stone was created by Daniela Einsdorf, an Überlingen artist who also belongs to a local group from southern Germany set up following the tragedy to promote relations with eastern Europe and Russia.
"The sculpture is very light and extremely appropriate. I really hope that people like it and feel that it is representative," said Herr.
Four years on, however, the tragedy continues to cast a shadow.
Herr explained that for Skyguide's 1,400 staff members, the crash and the killing were now part of the history of Swiss air traffic control.
"Some people have got over the accident and the killing, but for others it is still very much present," he added.
"Dealing with it is not always easy. But I think we are on the right track both here at Skyguide and in terms of our relations with the families of the victims."
Elsewhere a number of legal actions relating to the air crash are still ongoing.
In May the first civil lawsuit seeking damages, held at a regional court in Constance in southern Germany, concluded that Germany and Skyguide might have to pay millions of dollars in compensation to Bashkirian Airlines.
The judge declared that the way in which air traffic was organised by Skyguide at the time was the main cause of the collision, and events that night were "incomprehensible and unacceptable".
The German court is expected to make a final decision on July 27.
Two other civil suits are due to be heard in the same courthouse. International courier firm DHL and its 19 insurance companies are seeking compensation from Germany.
In another case the Swiss insurance company Winterthur is looking to reclaim $2.5 million that Skyguide has paid out in out-of-court settlements with the families of crash victims.
Skyguide has handed over a reported compensation package of between $100,000 and $150,000 per victim.
swissinfo, Simon Bradley
On July 1, 2002 a Russian passenger plane collided with a cargo jet over Swiss-controlled airspace above Überlingen in southern Germany, killing 71 people.
Skyguide subsequently admitted partial responsibility and a relative of three victims took revenge on a controller on duty at the time of the accident by stabbing him to death at his home in Zurich in February 2004.
A Zurich court found Russian architect Vitaly Kaloyev guilty of the intentional killing of the controller and sentenced him to eight years in prison. The final verdict is still pending.
In their October 2005 report, German investigators said the accident was due largely to negligence on the part of Skyguide, and partially the fault of the two Russian pilots.