Normally when I am searching for specific records to open, I use the record's ID. You should include the record ID as a hidden column in the listbox (if you haven't done so already). Then change your code to something like
Private Sub List0_DblClick(Cancel As Integer)
On Error GoTo Err_listbox_Click
Dim stDocName As String
Dim rst As Recordset, strCriteria As String
stDocName = "Edit Case Info"
strCriteria = "[ID]=" & Me![List0].column(0)
'the column number is whatever the ID column position is minus 1
DoCmd.OpenForm stDocName
Set rst = Forms![Edit Case Info].RecordsetClone
rst.FindFirst strCriteria
Forms![Edit Case Info].Bookmark = rst.Bookmark
Me![List0] = ""
Exit_listbox_Click:
Exit Sub
Err_listbox_Click:
MsgBox Err.Description
Resume Exit_listbox_Click
End Sub
After a specific record is selected from the listbox, you don't want to use a generalized criteria. I'm assuming that more than one record can be assigned to the same person.
Let me know how this works
Charity