This is a tragedy but not an unexpected one.
Just about any man can overpower just about any woman. This is just a matter of biology. Women go through the police academy, get a badge and a gun and expect those items to keep them safe.
I'll be the FIRST to admit, that a gun can be a great equalizer when it comes to an attack against a man. However, this police officer could not have had her gun out while handcuffing the rape suspect that ultimately shot her with her own gun.
Why would she not call for backup. The man she arrested basically had nothing to lose in the struggle so he put up a fight. She should have anticipated this and called for backup. I'm not saying it's HER FAULT but she is partly responsible for her own death since she willingly put her self in the situation. Obviously the suspect is responsible for his own actions.
As I've previously written though, total culpability can be 100% for each party involved rather than just 100% for the incident.