Thanks for the quick response, I did setup openVPN and PPTP on pfsense and I don't see any log associated to his account. our basic network setup is everything coming from outside our internal network will goes to the pfsense, so I assumed that all connection from outside the building will goes to the pfsense. I did not notice any abvious network change internally, because I thought maybe he setup a wireless router and this is the place where he login, but no there is no physical change on our network I don't see any hidden router or connection internally.
I am thinking my first resource to verify this is through the firewall which is the pfsense, assuming that he was trying to access our network from outside the building.