Sorry about this Benson, I did not read the category of the post.
I don't remember much about jbpm3 (used it in the past), but this class could help you:
http://docs.jboss.com/jbpm/v3.2/javadoc-jpdl/org/jbpm/taskmgmt/exe/TaskInstance.html#getActorId()
Regards,
Demian