Antoinette Frank

In 1994, Frank robbed and murdered a police officer, a 17-year-old man and 
a 24-year-old woman in New Orleans. Frank, a former police officer, committed 
the murders during the robbery of a Vietnamese restaurant where she had worked 
as a security guard. 

http://abcnews.go.com/sections/us/deathrow/deathrow_women.html

Officer Antoinette Frank: At 1:00 a.m. on March 4, 1995, New Orleans police 
officer Antoinette Frank and an accomplice entered a Vietnamese restaurant 
in east New Orleans, shot the off-duty police officer moonlighting as a 
security guard, and then executed a brother and sister who worked at their 
family's restaurant as they knelt on the floor praying and begging for mercy. 
The victims' brother and sister hid in a cooler and witnessed much of what 
transpired. Frank, who did not disguise herself, knew the family and had 
moonlighted as a security guard at the restaurant before, and even responded 
to their call for help after the incident, as though she knew nothing about 
what had transpired. She was quickly convicted and sentenced to death in 
September 1995

http://www.hrw.org/reports98/police/uspo94.htm