How to get the resource who made the change to a work item?

Hi,

Im using a BIRT report to show all work items that had a change in the "Time Spent" attribute. Im using the WORKITEM_CHNGS table, but the problem i have is that it doesn't return the name of the person who perform the change but the person who was the owner of the work item when the change was made.

This information is shown in the "History" tab of the work item, so it must be stored somewhere. Any ideas on how to do it? Im using RTC 2.0

Thanks