I tried all the suggestions, but still not seeing the records of when the report was deleted and by whom. The report was deleted after 8:00AM 05/15/19 and before 8:00AM 05/16/19.
I already opened a case with Splunk with diag file. Hope they find something.
If its a saved search /report you can try this, the user field will give you who deleted the report.
index=_internal method=DELETE sourcetype=splunkd* source="/opt/splunk/var/log/splunk/splunkd_ui_access.log" uri=*saved/searches*
if it is done via Splunk GUI or REST, then it will be audited at :
index="internal" method=DELETE sourcetype=splunkdui_access
2.If it was amended etc, you can see in index=_audit
3. if it is done via backend, hopefully you will have Operating System auditing? Like auditd or Windows Security Log?