Getting Deleted Record Id With a Custom Workflow

Hi,

I have a custom workflow to update a custom entity' two fields when you delete a row from the sub grid(another custom entity). The problem I am struggling is I can not get the deleted record id neither with 

Entity entity = (Entity)context.InputParameters["Target"];  
string id = entity.Id.ToString();

nor 

IWorkflowContext context = executionContext.GetExtension<IWorkflowContext>();
string id =  context.PrimaryEntityId.ToString();

context returns null all the time. Can someone please give me any suggestion about it.
Many thanks.