TRigger catch delete on cascade from different table

hi everybody!
Could you help me please?
How do i do to active a trigger (target is save the history from delete rows)
without catch the event from the table where has created
but catching the delete effect from a referenced value of other table?

For example

CREATE TABLEDocument
(
id_document INTEGER PRIMARY KEY,
id_user INTEGER REFERENCES User(id_user)
ON UPDATE CASCADE
ON DELETE CASCADE
);

CREATE TABLEUser
(
id_user INTEGER PRIMARY KEY,
username VARCHAR(20) NOT NULL,
pwd VARCHAR(30) NOT NULL,
email VARCHAR(30) NOT NULL
);

On Document table i defined a trigger
AFTER DELETE ON Document

On User table i excute
DELETE FROM User WHERE(condition);

So, when i delete a user from User table, the trigger rightly doesn't recognise
the DELETE because the recognise on Document.

Exists a way that let understand/catching at Trigger activing also in the case
of deleting on cascade from other table?

Thanks in advanced
Greating