"Does the journalist have their bank records?"
Translation:Apakah jurnalis itu punya catatan bank mereka?
The sentence has this meaning :
Does this one single journalist have the bank records of the other persons ?
So, it's just one journalist (3rd person singular).
"mereka" refers to the other persons (3rd person plural), not the journalist.
"mereka" is the possessive pronoun.
"mereka" is the owner of the bank records.