Custody period as utp for two cases.

My brother in law was arrested on may 2013 for economic offence while he was allegedly a director of a coop society. while he was still in custody, he was remanded by the CBI for commitment of another economic offence as director of another company in january 2016. both the cases are investigated by CBI . two firs have been filed and separate charges are being framed for both the companies. what will be the custody period as UTP for both the cases ? is it possible to club the period of custody for both cases ? i.e. from may 2013 for the second case also. please advice.