The “why” behind a vandalism spree that left cars spray painted with the number 68 remains a mystery, but police say they have pinned down the “who.”

Christopher W. Bolt, 18, of Sterling was charged Thursday with one felony count of destruction of property for an incident Monday involving a vehicle on East Staunton Avenue.

Police said the number has been painted on more than 50 cars in Ashburn, Leesburg and Sterling since April. Bolt has been “cooperative” with investigators, police said.

Authorities do not know the significance of the number, said Kraig Troxell, spokesman for the Loudoun County Sheriff’s Office. He said nothing indicates that it is tied to gang activity.

The painting was done to cars on residential streets and occasionally there was an “X” added to the numeral, Troxell said. He said the investigation is continuing.

Leads from the public led officials to Bolt, Troxell said.