48 Hours: Q&A with Vanessa Riebli, Johnson County Assistant District Attorney

(CBS) - On the morning of Sept. 8, 2010, Marti Hill was brutally attacked in her home on a quiet suburban street in Prairie Village, Kansas. The assault occurred when she answered her front door as she prepared to leave for work. The attacker was not a stranger. He was a handyman who had periodically worked for her family over a number of years. His name was Brian Pennington.

On that fateful day, Pennington lured Marti Hill to the basement of her home by claiming that there were repairs that needed to be made down there. As they reached the bottom of the basement stairs, he grabbed her by the throat. He then strangled, beat and slashed Marti Hill's throat three to four times. Marti Hill was left to die in her tiny, unfinished basement.

Marti Hill survived the attack and later identified Pennington as her attacker. Pennington was sentenced to 28.5 years in the Kansas prison system, but he has never told anyone WHY he committed this horrific crime.

Johnson County Assistant District Attorney Vanessa Riebli talks to "48 Hours" producer Stephen McCain about what it was like to prosecute this fascinating case.

Watch now: "48 Hours" Live to Tell: The Stranger You Know
Photos: Crime scene of savage early morning attack

Stephen McCain: One of the most haunting questions in the Marti Hill case is why? Why did Brian Pennington so viciously attack Marti Hill? Authorities were never able to establish a clear motive for the attack. As a prosecutor, how big of a hurdle was that for you?

Vanessa Rieble: While motive is not an element of the offense, it is something that we want to be able to present to the jury in order to give them an explanation as to why the crime occurred. I believe this enables them to better understand the case and helps them to convict the defendant. In Marti's case, we don't know the "why" of her story. However, given our forensic evidence and Marti's recollection of events we believed it was an issue we could overcome.

SM: Is it more difficult to convince a jury without a motive?

VR: Yes. In my opinion, jurors watch too much television related to criminal law and have expectations that we cannot always meet. One of those expectations is to fully understand everything and make sense of what happened. In "real life" criminal law, we can't always answer all of questions and this can impact our case negatively to the jury.

SM: You described Brian Pennington's sentencing hearing this way: "The most powerful part to me was when Marti stood up and faced the man that tried to kill her ... she said to Brian, "I was nothing but nice to you." And asking him, "Why did you do this to me?" And he just sat there. No response." Was that personally frustrating for you?

VR: Yes -- on a personal level because I knew that Marti desperately needed to hear from him why he did this to her in order to help with her recovery. Also, as a prosecutor I wanted him to step up and admit what he had done.

SM: Is there any recourse to make Brian Pennington explain himself?

VR: No. He never has to answer to Marti the "why" question under the criminal justice system.

SM: Would it have been possible to make it a condition of his plea deal that he would have to provide an explanation?

VR: Theoretically - Yes. Realistically - No. As I told Marti many times, even if he were to provide a reason there is no guarantee it is the real reason.

SM: In some ways, the "why" question is an impediment to Marti's complete healing. In your experience as a prosecutor dealing with victims, is there any advice you can give to help violent crime victims move on with their lives in the absence of answers?

VR: You have to find it within yourself to start the healing process and work through it day by day with no requirement or prerequisite to "get answers" from the defendant. I don't believe looking for answers from the defendant will ever provide the satisfaction or explanation that is needed. Most answers will be self-serving or half truths whether because of legal reasons or the inability to admit to themselves why they committed the crime. My advice is to focus on themselves, their family, their therapy and their friends and empower themselves to move beyond the event with no necessity of a logical explanation as to "why" .....because it likely will never happen.