How can I check which user deleted other users

There is a Last 100 Audit Events report that could possibly give you the answers as to whom and when, the why only the person who deleted the user can tell you. I had to edit the report to report on the time period as it was defaulted to the last hour. You can also play around with the amount of audit events you want to see.

Not getting required data, instead of Last 100 Audit event can I change to 100 to 1000 or more?

yeah it seems like it, click on "Edit Table" next to Last 100 Audit Events

Not getting...

Are users assigned to SW via Group on Active Directory or are they added via the User account management in SW? If you are using groups from AD, then its best to check on AD who removed the user from the group.

No, I created manually for Offline SW agent installation purposes.

You should be able to create an audit report. I can only suggest that you play around with the Last 100 Audit events report.

You have a similar issue before about node deletion and what I posted is to use the Auditing Events.  I think you opted to use a custom Query.  Instead of relying on custom queries, familiarize yourself with the default features of the product.

solarwindscore.my.site.com/.../Viewing-and-reporting-audit-events

ok, thanks for your time.

Thanks for the reminder, I was able to find details in the Message center.