Blocker did not identified

I got an issue related to lock.
Now the daabase was re-started and the issue is solved. But during investigation I did not get sucess to identify who were locking a table.

A table is used like this:

SELECT ID FROM TABLE_BLA
where id = :1
for upate;

The query did not return the result and looking for lock using this query :

 select s.sid, s.blocking_session, do.object_name,

    row_wait_obj#, row_wait_file#, row_wait_block#, row_wait_row#,     dbms_rowid.rowid_create ( 1, ROW_WAIT_OBJ#, ROW_WAIT_FILE#, ROW_WAIT_BLOCK#, ROW_WAIT_ROW# )
    from v$session s, dba_objects do
    where s.ROW_WAIT_OBJ# = do.OBJECT_ID

I saw the row_wait_obj#, ROW_WAIT_FILE#, ROW_WAIT_BLOCK# and ROW_WAIT_ROW# values.