Speaking in the House of Commons, Home Secretary Theresa May said: "Could I also extend my sympathies to the family of the 13-year-old girl who died following a traffic accident involving a police patrol car on Sunday night.
"This matter is being investigated by the Independent Police Complaints Commission."
More top news
Guillier conceded a "severe defeat" defeat to his supporters as the result came in.
The outage struck Hartfield-Jackson Atlanta International Airport at around 1pm local time, stopping all outgoing flights.
It will be a chilly day for many parts with the highest temperatures, about 10 Celsius (50F) in the far northwest.