The router should have a list of active and inactive ip addresses and mac addresses which have used it, within the admin login.
Take a look and eliminate his machines (PC, phone, tablet etc) the one / ones that are left are the culprits.
@Soul started
London Fixed Gear and Single-Speed is a community of fixed gear and single-speed cyclists.
@Soul
The router should have a list of active and inactive ip addresses and mac addresses which have used it, within the admin login.
Take a look and eliminate his machines (PC, phone, tablet etc) the one / ones that are left are the culprits.