To do so, we first need to determine the unique identifier (uuid) of an artifact in the deleted folder. To do this, open the baseline and right click on the artifact hyperlink and copy it's link address. In this url, you'll find a segment for "artifactURI=". You'll want to extract the uuid that appears following rm/resources. For example, see the bold text in the sample url below:
https://{host:port}/rm/web#action=com.ibm.rdm.web.pages.showArtifactHistory&artifactURI=https%3A%2F%2F{host:port}%2Frm%2Fresources%2F_gJwYlDuuEeWlGOQq0QQ_dA&revision=https%3A%2F%2F{host:port}%2Frm%2Fresources%2F_gJwYlDuuEeWlGOQq0QQ_dA%3Frevision%3D_gJxmszuuEeWlGOQq0QQ_dA&baselineURI=https%3A%2F%2F{host:port}%2Fjts%2Fbaselines%2F_U8iwYT9rEeWJZvQEjgRoQw

Use that uuid to form a url like the following (substituting in your own server details):

https://{host:port}/rm/revisions?url=https://{host:port}/rm/resources/_gJwYlDuuEeWlGOQq0QQ_dA&accept=*&private=true

Place this url in the address bar of your browser. This will return a revision feed for the artifact. The topmost <entry> represents the last time this artifact was modified and consequently the value shown for "author" and "updated" will indicate the user and time at which the artifact was deleted.

Something very similar can be done for folders directly as well. However it's more complicated to get the uuid of a deleted folder than it is an artifact, so if you do not know that uuid, there are several more steps required (including placing the server into debug mode) in order to get the folder uuid.

Admittedly this is a lot of effort. I do believe there are enhancement requests to have RRC/RDNG provide better support for archived data, but I have no direct knowledge of any particular plans in this area.

That said, I have created a tool/utility to perform the above (and also the harder folder case) that can be requested from IBM Support. But please note this is simply a diagnostic aid. It is not intended to become or replace any potential product features and is not intended to provide any sort of restoration capability. It merely tries to determine who archived a particular resource.