I am very keen to trace this vehicle and would appeal to anyone with information to give my team a call.
Did you see the car in the area of the murder at around midnight on Saturday into Sunday (30 December)?
If you believe you may have seen this car anywhere subsequently, I would also urge you to get in touch as soon as possible.
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George Michael died in December last year at the age of 53.
PC Keith Palmer, 48, stabbed by Khalid Masood while on duty in the grounds of the Palace of Westminster last Wednesday.
Those gathered on the bridge fell silent at 2.40pm - the time the first call was made to police exactly seven days ago.