In some examples, a system detects an accident involving a first vehicle, where the detecting is based on an accident indication received by the service over a network from a second vehicle not involved in the accident, the second vehicle different from the first vehicle, and where the accident indication from the second vehicle is responsive to messages received by the second vehicle from other vehicles. In response to the detecting of the accident, the system verifies that the accident occurred by sending, from the service, queries to a roadside unit and a third vehicle, and receiving, at the service, responses to the queries from the roadside unit and the third vehicle, the responses containing event data collected by the roadside unit and the third vehicle of events in a vicinity of the accident.