The tree was embedded in the front of the bus and emergency crews were using cutting equipment to gain access to one side of the vehicle.
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The reason for the shooting is unclear, but local media have reported it may be a settling of scores between criminals.
Most parts of the country will experience near unbroken sunshine after a chilly start to the day.
As the investigation into Khalid Masood continues, former acquaintances tell of violent incidents in the murderer's past.