Dear Prashant,
Lot of seniors have given their advices however, here are my two cents.
Your confusion is because your focus is on persons. Shift your focus to the incident. We order domestic enquiry to investigate the incident. Absence from work, abuse to the superiors, theft of company property etc all these are incidents that merit investigation.
In the course of enquiry, Enquiry Officer (EO) should chart out the sequence of events and go on investigating. As and when required, EO can summon required employees to depose before the enquiry and record their evidence. While investigating focus should be on:
a) What happened?
b) Where it happened
c) When it happened?
d) Who were involved in the incident? Who were internal parties? Who were external parties? Was there any agent provocateur?
e) Was there injury to the any person?
f) Was there damage to any company property?
g) Did the incident tarnish image of the company?
h) Was there any transgression of laid down rules, regulations, SOPs etc?
Ok...
Dinesh V Divekar