SQL & PL/SQL :: Case Statement In Where Clause

select empno,ename,deptno,employee_status from emp,dept where emp.deptno=dept.deptno and
( employee_status in(Case employee_status when {?Status}=1 then 'A'
when {?Status}= 2 then 'T'
When {?Status}= 3 then 'A'||','||'T'))
OR ( end_date >= {?START_DATE}
AND end_date <= {?END_DATE}
)
)

Since when i pass employee_status as input 1 it have given me 4 records. When I pass employee_status as input 2 it have given me 3 records. When I pass employee_status as input 3 it should give me 4 records + 3 records=7 records.

4 records for employee_status 'A'
3 RECORDS for employee_status 'T'
7 records for employee_status 'A' AND 'T'

How I should write a query to get 7 records.