>>> crimes force the police to change how they protect us. tonight we will go in one such case that shook dallas . this involves a brutal crime. the attack of a woman, allegedly by her ex-husband. what makes the case unique, as you'll hear is the response by a 911 operator to the victim's horrifying pleas for help and the mystifying response by dallas police . kate snow tonight unravels a tragedy that turns out to have twists and turns no one could have imagined.

>> lift your hands toward heaven and let's worship god .

>> reporter: vicki cook is the mother of four daughters. it is a close-knit family that worships together every week. last august her eldest daughter didn't show up for church. the family was worried her ex-husband had been in and out of jail for assaulting her. her mother vicki and two sisters say the threats were getting so bad deanna had replietd called 911 for help.

>> she moved multiple times to get away. he always finds her. he always stalks her to find out where she is.

>> i heard him tell my daughter that he was going to kill me. he was going to kill her daughters and then he was going to kill her.

>> when she didn't show up on that particular sunday, what was your first thought?

>> something's wrong.

>> they rushed to deanna 's home and discovered water was pouring out of the house. when deanna didn't answer the door, her mother called 911.

>> may daughter has been missing since friday. she is 32.

>> have you called all the jails and hospitals?

>> reporter: at first the operator refused to call police .

>> ma'am, can you just send the police over here.

>> no, ma'am.

>> i said i need for you to send somebody right now. something is going on here and i need to get in this house.

>> do you think somebody did something to her.

>> yes, i do.

>> while she was on the phone i was looking for ways to get in.

>> you kicked in the window.

>> yes.

>> when i went in the house the water covered my ankles. there was just that matter much.

>> water is all over the floor.

>> i just looked and said something is going on in here. what's going on and i walked through her house and i looked at the door and it had been kicked.

>> somebody happened in here.

>> okay, ma'am. i'm sending police .

>> somebody did fighting in here. what's going on? so i walked around her room and i looked at all of the stuff on the floor and i walked in the bathroom --

>> okay.

>> so that's when we found her when she was in the bathtub and i mean it was horrible.

>> deanna was dead in the overflowing tub. the tap still on. it was a heart-breaking end for a single mother who called her own mother twice a day.

>> we stand with them.

>> reporter: deanna left behind two daughters. aniya is 14 and anicea just turned 16. they were all in morning but their grief turned to anger when they learned on the day she died, deanna called 911 herself as she was being attacked. the family wanted to know why couldn't police save her.

>> there were so many questions to be answered wane couldn't get any information at all.

>> reporter: at police headquarters, they say investigators refused to release any details.

>> we were angry. we were confused. we were frustrated. we were clueless.

>> we were wondering what they were hiding.

>> reporter: while they were talking to investigators, they overheard deanna 's final call to 911 being played in the next room.

>> dallas 911. what is your emergency?

>> i put my ear to the wall to try to listen closer to try to see if it was deanna .

>> why are you doing this?

>> hello.

>> this is the 911 call police wouldn't release to the family because of the ongoing investigation. but the family wants the world to hear how deanna fought for her life as an operator listened.

>> you need police , fire or ambulance? i need an answer.

>> you can't deny she is begging for help.

>> police .

>> no!

>> she is screaming for help.

>> stop it.

>> eight and a half minutes in to the call deanna is still pleading with her attacker.

>> somebody call police .

>> reporter: then the call is eerily quiet.

>> you hear her last breath on that tape.

>> reporter: the family was finally getting answers, but not from police . a local reporter told them it had taken officers 50 minutes, nearly one hour to respond to deanna 's call for help .

>> you knew the call came from her. why didn't you do what you are supposed to do?

>> there's no sense of urgency. there's no -- it happens a lot in our neighborhood actually. in our zip code the police take their time to get there but to protect and serve we don't get that in our neighborhood.

>> reporter: to deanna 's family, it sounded like she had died while she was on the line with the 911 operator .

>> what does it say to women in this city when it happened?

>> it would say to a woman that these aren't priority calls.

>> paige fling is one of the head of a family violence centers.

>> it would say to a woman sometimes they are going to get away with it and maybe you do everything right and you still die.

>> reporter: the 911 call center has been beleaguered for years, understaffed and overwhelmed by 2 million calls annually. last year, 30% of the operator positions were unfilled. at the same time, incidents of domestic violence were at a record high.

>> in 2011 , we had ten domestic violence murders. in 2012 , we had 26. so we know we have a problem.

>> reporter: and yet when victims like deanna cook called 911, unless operators knew a gun was involved or someone was already injured the training manual instructed them to enter a code that did not give those calls the highest priority.

>> do you wish she had called somebody else that friday?

>> that was my main question, why did she even call the police ? she knows they take their time. she knows. i thought she knew what i nuchl why didn't she call our cousins, us, why did she call the police first and that's horrible for a woman experiencing violence to think she can't call the police first.

>> reporter: the cook family filed a wrongful death lawsuit against the city of dallas . the first person named in the suit, the 911 operator tanita hopkins.

>> dallas 911. this is tanita. what is your emergency.

>> i can't imagine hearing that voice on the phone and not yelling at the dispatch, murder in progress. murder in progress.

>> that's what i would have called it, murder in progress.

>> chilling unbelievable story and when kate snow continues her report, the 911 operator at the end of that line, that awful day, speaks for the