Multiple Web Leads from Same Customer Different Sources

Need to find a way to be able to intuitively link leads for the same customer, that come in from the same or different sources, so that they are going to the same salesperson. IE: Lead comes in from source1 for John Doe (johndoe@email.com, 555-111-2222). Five minutes later, lead comes in from source2 for John Doe (johndoe@email.com, 555-111-2222). This time, because that source domain is set up for round robin, the lead went to another salesperson. Need to find a way for the software to know that the second lead is already linked to a different salesperson.