Police in the United States are trying to determine if a man shot dead at a petrol station near Washington could be the ninth victim of a sniper on a week-long killing spree. Investigators in the Virginia town of Manassas said it was too early to know if it was linked, but a team investigating the killings has described Wednesday's incident as "very similar". The authorities are looking for a white vehicle that was spotted leaving the scene. The series of attacks, which have been linked by ballistics experts, has killed six people and injured two in the area around the capital, Washington DC.