It is possible to use the lookback API to find who deleted a work item even if you don't have the object ID of the work item.
Release : SAAS
You will need your workspace object ID. Use the following article to find that:
https://knowledge.broadcom.com/external/article/47763/rally-find-object-ids-of-current-worksp.html
The next consideration is that lookback API does not use formatted IDs with the letter preceding the ID. Instead, it uses an unformatted ID which is numeric in value only. So you will need to query for that numeric value only however you will enter the work item type as the _TypeHierarchy attribute.
The general syntax of the query will appear as follows:
https://rally1.rallydev.com/analytics/v2.0/service/rally/workspace/<WORKSPACE_OID>/artifact/snapshot/query.js?find={
"_UnformattedID": <UNFORMATTED_ID>,
"_TypeHierarchy": "<WORK_ITEM_TYPE>",
"_SnapshotType": "DELETE"
}&fields=["_RevisionDate","_User","Name"]&sort={'ObjectID' : -1, '_ValidFrom': 1}
Example:
Assuming a workspace object ID of 987654321 and a formatted ID of F4567. We know this is a Feature in our environment. So we populate the request as shown below:
https://rally1.rallydev.com/analytics/v2.0/service/rally/workspace/<WORKSPACE_OID>/artifact/snapshot/query.js?find={
"_UnformattedID": 4567,
"_TypeHierarchy": "PortfolioItem/Feature",
"_SnapshotType": "DELETE"
}&fields=["_RevisionDate","_User","Name"]&sort={'ObjectID' : -1, '_ValidFrom': 1}
In the Results object of the output, we will find three attributes; the _RevisionDate which indicates when it was deleted, the _User attribute which is the object ID of the user that deleted the work item, and the Name field which gives you a better idea if this is looking at the right work item or not.
The next step is to identify the user based on the object ID. This step requires workspace admin or better permissions in Rally. Using the following URL, you will place the object ID at the end of the address which will bring up the admin page for that user.
https://rally1.rallydev.com/#/detail/user/<USER_OID>
Example:
https://rally1.rallydev.com/#/detail/user/<USER_OID>