On the night of July 1, 2002, Russian architect Vitaly Kaloyev was working in Barcelona waiting for his wife and two children to fly in and join him. They never arrived.
Two years later, he knocked on the door of the man he held responsible and st*bbed him to d*ath in front of his family.
At 11:35pm over the German town of Überlingen, Bashkirian Airlines Flight 2937, carrying 69 people including 46 Russian schoolchildren on a UNESCO-organised trip to Spain, collided with a DHL cargo flight.
Nobody survived on either aircraft.
Kaloyev's wife Svetlana and their two children, ten-year-old Konstantin and four-year-old Diana, were among the dead.
He flew to the crash site and participated in the search for bodies himself, finding his daughter's pearl necklace in the wreckage.
Diana's body was intact, having been broken by trees on the way down. Konstantin's body hit the asphalt in front of a bus shelter.
He spent the following year sleeping at his family's graves and building a shrine to them in his home.
He rejected compensation offered by Skyguide, the air traffic control company. He hired a private detective to locate the specific controller on duty that night.
On February 24, 2004, Kaloyev travelled to the Swiss town of Kloten and sat in the garden of Peter Nielsen's home.
Nielsen came outside to ask what he wanted, accompanied by his young children. His wife was still inside when she heard a scream.
Nielsen was st*bbed multiple times and d*ed within minutes, in front of his family.
There is a brutal footnote to the question of blame. The official investigation report, published two months after Nielsen's de*th, largely exonerated him personally, finding that systemic failures at Skyguide, including leaving a single controller to manage two workstations alone at night, were the primary cause of the collision.
Four Skyguide managers were later convicted of negligent homic*de.
Kaloyev was sentenced to eight years but released after three and a half. He returned to Russia to a hero's welcome and was appointed deputy minister of construction of North Ossetia.
Nielsen's family received no such recognition. He was 36 years old when he was ki*led.