How to retrieve ContactID related to Lead

Dear experts,

we are using the BeforeSave-Event in a LeadXBO. We need to find out the Contact that is defined within the lead triggers the BeforeSave.

Using Party.BusinessPartner finds only BusinessPartners of the following RoleCategoryCodes:

31 – Prospect Party

39 – Employee Respons. Party

46 – Sales Employee

An entry with RoleCategoryCode 59 (Code for Contact) does not appear. Eventhough the Lead linked to a Contact.

Does anyone know have an idea how to get the ContactID related to a Lead?

Thank you very much in advance.

Kind regards

Lars