Officials Think Clear Motive Unlikely in Newtown, Conn., Shooting

Prosecutors release findings of year-long investigation into Sandy Hook school shooting.
3:00 | 11/25/13

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Transcript for Officials Think Clear Motive Unlikely in Newtown, Conn., Shooting
This is a special room. And Democrats -- New York with his ABC news digital special report that chilling details of the new town shooting outlined in a 48 page report. Police and prosecution of Danbury Connecticut releasing their timeline. And the background on the sandy hook -- for shooting where twenty children and six adults were killed. In less than eleven minutes the motive of the shooter Adam lands are inconclusive. According to the report. ABC's Aaron deter ski joining us now for more on the report and the details that it contains -- -- this this report essentially gives timeline. Of the events inside the school -- some very frightening details are out like Dennis. It's really the very first official account after nearly a year since the shootings at sandy hook elementary school. And it relives all of the horror of that day and it reveals stand at. All of the children 21 graders and the six women. Who were shot dead at sandy hook elementary school were killed in the span of less than eleven minutes and also reveals that there was a six minute gap from the time. Police officers first arrived on scene at a time they actually entered the building though it offers no specific explanation as to whether there was actually a delay. Whether the officers entry time simply wasn't recorded or whether they were simply -- operating on the assumption. But there was another shooter and they they needed to to wait before they rushed it into a building where they could have faced -- even more gunfire. The report also details more about the background of the gunman Adam Lanza. It says he had significant mental health issues but he knew what he was doing was wrong and he had control of his actions. To dictate the outcome that he wanted including killing his taking his own life and so the report concludes. That's the question of why. May never be answered conclusively why did Adam -- to kill all those people why did -- choose sandy hook elementary school it may simply turn out it was the closest school to where he lived. The other aspect of this report Erin is the fact that it outlines -- video games in fact the state thinks that in fact. He could've been an influence. In his behavior you know they they don't come right accountants say it but they do suggest. The first of all they make clear that Atlanta was an extensive gamer. They've done well a lot of background checks to do indicated as much and they also listed and -- photograph of the photographs of all the games that he had. In his home the report by the way includes photographs inside the home of this of this mass killer. And you see the collection and you see what he was playing. And and the way the report reads it almost suggests that if that Atlanta was using Cindy cook has his own personal video game where he was the storm -- of people think that. Well look what he did he use earplugs. And that's something he may have picked up by a video game. He also -- -- frequently changed his magazines frequently before the -- they ran out he had. That there were thirty rounds and in a magazine. Oftentimes -- -- after using up just fifteen of those bullets and gamers would know. That you never enter a new room unless you have a fully loaded magazine. They also talk about the planning Dan. The extensive planning that Adam -- used to to to to do this he had been in the vicinity GPS records show of sandy hook elementary school the day before. It seems as if he had written a cartoon book where he inpatient characters killing one another. And this was years before he had an obsession with mass murder including the Columbine shootings and all of this is laid out. A forty page report that takes you back to what was just an awful awful day in American history. It was an almost hard to believe almost one year ago the details. Of that -- just out. Aaron thank you for that I want to bring in homicide prosecutor and a senior -- Nazi. For a legal perspective on this and and and -- -- if the shooter. And -- -- is dead at the state still need to make a case against him. He didn't need to but often in cases where. There is no prosecution there is no arrests as here and that such interest -- parkinson's here mean that. Nation understandably cares has been riveted with this case because of the magnitude of -- inflicted by Adam -- so while they didn't need to. They often put out -- report trying to give some. Transparency. To the system to show the investigation that was conducted. And also to sometimes -- some answers some closure hopefully unfortunately we can do nothing to. -- those affected the families the friends the town itself of the many victims in this case. But sometimes giving people some sense of understanding of the work that was done can be helpful on I'm sure that is why the State's attorney chose to do that in this case. If you can't explain some of the language that was used in this report because essentially says that Adam lands -- committed 26 counts. Of murder under special circumstances. Who what does that mean. Well that is part of that right there there are sometimes types of cases are termed a special circumstances want to hear the sheer number of victims. To his attack you also have the ages of the victim twenty. First graders which right there makes it a different different more. Brutal horrible crime in and of itself than those of the type of things that his legal jargon. For the additional factors that are being looked at and would have been looked at -- influence -- charges had Lanza survives. The other point about this is the report indicates it was a premeditated act. This is clearly. As has just said before by Aaron he had on their TD before -- -- to the school with GPS. He had long list of his obsession with mass murder and of specifically. School. Killings that he talked about you had the collection of the ammunition that he brought him and the number of weapons and things that show that this is not something that he woke up that day. And just -- out and did this was thought out and although unfortunately they could not give a clear picture of his motive. It was something that he had obviously planned sometime before and the planning into that at the -- -- the -- report also point out that Adam Lanza. Had mental health problems as well. -- a horrible combination going on here you had this young man with severe. Types of mental illness and various things working together coupled with. The obsession that he had with mass murder and he also had a familiarity and access to firearms and that is a terrible in this case lethal combination. And he had mental illness that although the report is not specific than talking that various things in his mother said and that. Had been diagnosed over the years that different things worked together and he certainly seemed to be becoming more of -- -- or more clues at this time went on. Given the purpose of this report that how significant is it that it found that the motive. Essentially -- inconclusive. I don't know how significant it is because whether we knew the motive or not it wouldn't change the heart that Adam -- inflicted that -- but sometimes it helps with the understanding. Whether it is in trying to prevent things like this in the future just give some sort of closure or healing. To those involved in those that have survived that's the reason why people like to know the motive -- can help us that in of itself unfortunately will do nothing to. Change what happened that fateful day. In addition to the healing process was it necessary -- in order for police to. Legally closed the case. -- -- want thing that always -- down that needed to be answers to make sure there was no one else involved or that. Knew about and helped him. Planned this or carry out his attacks -- every anyway and wallet was suspected from the beginning that he acted alone. Certainly that is something -- be very important to know because if there wasn't a threat left out there of someone that had some. Small part or role -- -- that's -- need to be held accountable legally and also you wouldn't want to protect the public. From that individual in the future so that was an important piece for the investigation to move forward although Adam -- -- killed himself that day. Our homicide prosecutor and a -- a -- -- thank -- so much for your time we you have the complete report right here on For now I'm -- -- -- in New York with this ABC news digital special report.

This transcript has been automatically generated and may not be 100% accurate.

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