Now some of those questions have been answered.Chinese authorities said Saturday that the pilot, the aircraft's only occupant, was killed in the crash. Thirteen people on the ground were injured, although officials have not said whether they were inside the tower or struck by falling debris.The aircraft hit the 528-metre CITIC Tower — better known as China Zun — shortly before 6pm on Friday. Earlier reports describe how the collision shattered windows near the top of the skyscraper and triggered an immediate security lockdown around one of Beijing's busiest commercial districts.The physical damage turned out to be less severe than first feared. Officials said two exterior glass panels were broken, and firefighters quickly put out a small fire caused by debris that fell to the ground. The focus has now shifted from the building to the aircraft itself.How it ended up there remains the biggest mystery.Flight-tracking data reviewed by Reuters shows the single-engine aircraft taking off from an airport east of Beijing before heading towards the city centre. It was later identified as a Sunward SA60L Aurora, a light sport aircraft commonly used for training and recreational flying.That route has drawn particular attention because Beijing's airspace is among the most tightly controlled in the world. Flights over the capital are heavily regulated, making crashes involving small civilian aircraft exceptionally rare. Investigators have not said whether they are examining mechanical failure, pilot error or another cause.As investigators began piecing together the flight, security remained tight around China Zun.Authorities formally confirmed the casualties almost a day after the crash and said an investigation is underway.The aircraft is believed to belong to a Beijing-based general aviation operator, but officials have not confirmed why it was flying over the capital or what its intended destination was.