OpenBSC implementation problem

Dear Sir or Madam, We are students from Poznan University of Technology in Poland.We want to develop our GUI enhancement for OpenBSC project.It's about adding and deleting users registered in network. We have already implemented adding logged users, but we couldn't make this part of program, which is responsible for deleting users when they have already logged out. Could you give some advice, where to find appropriate place in the source code in OpenBSC. Thanks in advance. Best regards Marek Świąder