Simulate Delete Operation Through Using Update On Trigger

I'm trying to simulate a delete operation through using an update on a trigger my tables are

CREATE TABLE EMPLOYEE (
LNAME VARCHAR(15) NOT NULL,
SSN CHAR(9) NOT NULL,
salary FLOAT,
dno INT NOT NULL,
vst DATE,
vet DATE,
PRIMARY KEY (Ssn));
[code]....

What I want to do is whenever there is an update on vet( valid end time) in employee, delete the values from the employee table and insert the old values from employee into the emp_history table along with the new value for vet. Here's my trigger

CREATE TRIGGER trig4
AFTER UPDATE OF VET ON EMPLOYEE
FOR EACH ROW
BEGIN
INSERT INTO EMP_HIST VALUES( : old.LNAME, : old.SSN, : old.salary, : old.dno, : old.vst, :new.vet);
DELETE FROM EMPLOYEE WHERE(SSN = :NEW.ssn AND vet IS NOT NULL);
END trig4;
//ignore the space between : and o as it makes a smily

The problem is I get an error for a mutating change, what I'd like to know is if the above trigger is possible, and if so how to implement it without giving me an error. I mean it makes sense syntactically and logically(at least to me).