He was the station"s chief correspondent in Asia. He reported from several wars and disaster areas. Author Scott Taylor, who describes himself as a “maverick war reporter”, described working beside Horner while they investigated the killing of civilians in Kosovo, during its civil war with the former Yugoslavia.
On 11 March 2014, Horner was shot dead in a street in Kabul in execution-style.
The Washington Post quoted another Swedish journalist, Terese Cristiansson, who described Horner as a “a legend,” and “one of the best we have ever had.”.