Try this, you also need to specify a return type
CREATE OR REPLACE FUNCTION crimes_tied_officer(FK1_WITNESS_TYPE_ID VARCHAR2) RETURN VARCHAR2
AS
lv_witness_check VARCHAR2(40);
BEGIN
IF FK1_WITNESS_TYPE_ID = '800' THEN
lv_witness_check := 'External Observation Witness';
ELSIF FK1_WITNESS_TYPE_ID = 801 THEN
lv_witness_check := 'Expert Witness';
ELSIF FK1_WITNESS_TYPE_ID = 802 THEN
lv_witness_check := 'Partner or Spouse';
ELSIF FK1_WITNESS_TYPE_ID = 803 THEN
lv_witness_check := 'Police Officer';
ELSIF FK1_WITNESS_TYPE_ID = 804 THEN
lv_witness_check := 'The Accused';
ELSE
lv_witness_check := 'No Witness Type Selected';
END IF;
RETURN lv_witness_check;
END;