Obsession, Part 6

>>> the case against sheila davalloo was loaded with motive. love, rage, obsession. but the prosecutor needed evidence that put her at the scene of the crime . and that's where a cut on sheila 's hand came in. sheila 's friend, tammy may, testified she noticed the ugly gash just a few weeks after anna - lisa 's murder.

>> i was like oh, my goodness, what did you do? she said she cut it on a can of dog food .

>> reporter: but what if she cut herself during the murder and left some dna behind. police checked sheila 's dna against some blood found at the crime scene . investigator mcginn ty could hardy contain himself.

>> do you remember your exact words?

>> his exact words, "we've got her."

>> sheila 's dna was found on a drop of blood on a sink handle in anna - lisa 's bathroom.

>> there is only one explanation for that. that is she did this crime. it is consistent with guilt and only guilt.

>> but it was just one tiny drop. was that enough to convince a jury?

>> i'm claiming my innocence.

>> reporter: not if sheila davalloo had her way.

>> this is a case where i am being accused of killing somebody.

>> reporter: as sheila davalloo presented the case for her own defense, she boiled it down to this. the state's case is flimsy, the evidence isn't there, and i'm not the villain they're making me out to be. with the respected public defender assisting, she listed the weaknesses of the prosecution's case.

>> no hair evidence.

>> reporter: the fact is from that terrible scene of violence and death --

>> no fingerprints.

>> reporter: there was no physical evidence with the exception of that one sample of dna --

>> search of my car yielded nothing.

>> reporter: that puts sheila in anna - lisa 's apartment. and even that couldn't put her there on the kday of the murder.

>> did the state prove to you that i was there on that day? they can't do that.

>> reporter: what about the 911 call that supposedly put her just a few blocks from the murder? the prosecution said the caller was probably the defendant. people who knew sheila testified it was hard for them to tell.

>> parts of it sounded like sheila and then a little part of it didn't sound like her.

>> when you heard that 911 tape, what did you think?

>> i couldn't really be sure.

>> reporter: and her lack of an alibi, sheila said there was nothing suspicious about the fact that she left the office the day of the murder because she left the office all the time.

>> on september 30th , i left work for four hours. on october 2nd , i left work around the same time for two hours.

>> reporter: she argued that once the police settled on her, they lost interest in any other suspects. she called gary riley , the petty criminal who had been seen in the area the day of the murder. he said he saw a fight going on between a woman and a man near anna - lisa 's apartment the day she was killed.

>> and i seen a lady and a guy arguing.

>> reporter: as for the attack on her husband that culminated here at the westchester medical center , sheila said it had nothing to do with anna - lisa raym raymundo or nelson sessler. she told us she had been depressed, abusing prescription medication and out of her mind when she stabbed paul . when she faced her ex-husband in court, she implied that she had been mentally impaired.

>> you stated that when i lunged at you, i looked distressed.

>> correct.

>> and you have previously stated that i looked kind of crazy at that time?

>> crazy, angry, correct.

>> what was that like to sit on the stand and be cross examined by sheila ?

>> it was weird. who knows what she's going to say.

>> she even asked paul , the man she stabbed, to comment on her supposedly gentle character.

>> and you have said that i never wished harm on other people, even those i disliked?

>> correct.

>> after the ex-husband, she moved on to the ex-lover, telling the jury she was never hung up on nelson sessler.

>> we had a summer fling. summer fling over a year before miss raymundo was killed.

>> and when sheila davalloo finally faced nelson sessler during her cross examination --

>> good afternoon, mr. sessler.

>> she seemed ready to throw him right under the bus, reminding the jury that he had once acted like he had something to hide.

>> you had lied to the police?

>> yes, i wasn't forthcoming to the police.

>> and what was the nature of that lie?

>> i hadn't told them that you had been my girlfriend in the past and we had a relationship.

>> right. and you did that why?

>> i didn't want you to go through the ordeal that i had gone through.

>> reporter: and then without presenting any evidence to back it up, she suggested nelson might be the killer.

>> on the day of miss raymundo's murder, mr. sessler, you had a swollen red knuckle, a red mark on the side of your face wrapping around your ear and scratches on your back, correct?

>> not to my knowledge.

>> reporter: over the two and a half week trial, the jurors heard the testimony of an ex-lover, an ex-husband, and hours of technical testimony about evidence, dna and a woman's voice, and then the jury got the case.

>> i refused they would not find her guilty.

>> but the prosecutor prepared your family for that possibility?

>> yes, he did.

>> reporter: a day passed. no verdict. on the second day, the jury came back.

>> will the defendant, sheila davalloo , please rise and face the jury. what say you, mr. foreperson. is she guilty or not guilty?

>> guilty.

>> reporter: guilty of murder in the first degree. two months later, anna - lisa 's got their say at sheila davalloo 's sentencing.

>> i would have repeated nightmares of seeing anna - lisa desperately crying out to me for help.

>> she broke my heart. our family will never be complete again.

>> reporter: and then it was sheila davalloo 's turn.

>> i'd like to ask some things for god, thank my family for their continued support.

>> she thanked everybody. she thanked the prosecutor for being an able adversary. i'd like to thank everybody in the department of corrections in new york and connecticut.

>> she stood up there as if she'd won an award.

>> reporter: she even addressed the raymundos.

>> i pray for them and hope that this punishment your honor will hand down today will bring them some kind of closure.

>> she made it sound like i didn't do it, but if you're going to give me this sentence, i'll do that for you. i mean that's the sheer arrogance.

>> reporter: in the end, the judge sentenced her to 50 years. but here's what the jury was never told. at this point sheila davalloo was already serving 25 years in new york for the attempted murder of her ex-husband. when that term is finished, she'll be sent to connecticut to start serving her sentence for anna - lisa 's murder. for now she is working on her appeals. the case has created an unexpected bond between paul cristos and anna - lisa 's parents.

>> we are very grateful to him.

>> in fact i told him i almost am not happy that you got stabbed but on the other side if you didn't get stabbed by your wife, anna - lisa 's case would have been a cold case .

>> i try to make them feel better and i said what's a little stabbing between friends . it was a paring knife, whatever.

>> i tell people what happened and everybody is like this is what you would see in a movie. i still find it hard to believe that it happened.

>> you look just like her.

>> bernadette and her husband now have three children that brought life back to this family.

>> for a pine cone to grow, it needs aer f foforest.

>> their first born was given the name annalise. she's funny, smart, just like her aunt.

>> what do you want people to know most about your sister, anna - lisa ?

>> my sister was one of the most loving people that you could ever meet. everybody that she came in touch with has wonderful memories of her.

>> you could picture her as princess or climbing a mountain or you could picture her playing tennis.

>> she would always want to be the best at everything she did, and she was.

>> that's all for this edition of "dateline." we'll be back again next friday at 10:00 , 9:00 central. and i'll see you tomorrow on "today." i'm lester holt . for all of us at nbc news, good night.