1. A method for reconstructing a trajectory at a site by means of a processing server connected to a set of cameras and having access to the video recordings from these cameras, the method comprising: implementing a 3D visualization application by the processing server, wherein the 3D visualization application is based on virtual reality and augmented reality based on: a static model of a 3D representation of the site; and a dynamic 3D representation database; wherein the 3D visualization application is configured to: determine, in the 3D visualization at a moment T0, the location of an object considered to have been left unattended at the site by an owner, in response to a first instruction from the user; select at least one camera which is best-positioned for displaying said object, wherein the selection of the best-positioned camera comprises: determining three-dimensional coordinates of a point of impact of the owner with the ground based on a click made on a 2D monitor displaying a recording currently being viewed; calculating the three-dimensional coordinates of the point of impact of the owner with the ground in the 3D visualization based on a bijective function between the 3D visualization and the 2D monitor, and determining the best-positioned camera based on the calculated three-dimensional coordinates, access a video recording from the determined best-positioned camera so as to display the recording at a moment t prior to T0, t is determined in response to a second instruction corresponding to the moment when the object was left unattended by an owner; and activate a method for tracking the owner via the recordings from the different cameras from the moment t to the present moment so as to determine the current location of said owner.