dennis murphy: "and then there were three."s, >>> then there were three. after chasing down hundreds of leads over four decades, the suspect list and michelle martinko's murder narrowed to three brothers living in iowa. when you run the computer check, criminal records? >> no. >> they are leading respectable middle-class lives? the family name was burns and all were adults in 1979 but did not seem to have a connection to michelle martinko. the investigator and two colleagues decided to secretly collect dna from all three. this is when you become a double agent. its shifting gears. >> it is. >> they track the brothers starting with the middle brother. a married father of three, he sold farm equipment in manchester. about a 15 minute drive from cedar rapids. >> we collected his dna from is trying to goes to the state lab. they told us, he is not your suspect. the next brother was donald. >> oldest brother donald was a father of three and had five grandchildren. he lived in davenport, iowa, and the manager of a lumber yard before

dennis murphy: everywhere the melendis looked, there was shannon's face.ter's missing posters blanketed her college campus. >>> everywhere they looked, there was shannon's face. their daughter's missing poster blanketed the college campus. >> that's all i could think of is where is she and is she okay? >> reporter: as the investigation started, police told reporters they were looking at two possibilities. >> either she left on her own our somebody grabbed her. >> whether shannon left on her home, they told investigators they were wasting time. she would never ever run away. she didn't run away from anything. >> reporter: they used the media to spread that message, hoping attention focused on the case would yield answers. >> i'm somebody who loves my daughter, and i want to do whatever i have to do to get this thing happening. >> so you think to get anything going, it needed your intervention and your passion and your concern? >> well, i'm a pain. i do what i need to do, and i don't care whose toes i step on. >> reporter: the only thing that made sense was

dennis murphy: lovely gazed out a hotel window and waited for news of her missing son.s crowded out the quiet. >>> lovely gazed at a hotel window and waited for news of her missing son. memories crowded out the quiet. pravin, a chatty and energetic child was always in motion from the time he was little. singing. dancing. running. he had made varsity on his high school track team. >> his cross-country coach said i don't know any kid who can run that fast and talk and cracked jokes. >> personality? >> goofy and funny. never held a grudge, ever. >> his real dream was to become an fbi agent. the criminal justice program at southern illinois university was well regarded, and there was something else the university was known for. >> when we looked at the college, my husband said, that's a party college. he said which college is not a party college? >> a party was the last place pravin had been seen. did he fit into that party crowd? >> we head a lot of his friends who told us he did party with them on a regular basis. >> drink until they got sloppy? >> he did consume alcohol

the 60 need to hide trashy is one of the biggest in denny murphy, i is looking for objects that she might be able to sell for extra income. josh, because own around $300.00 rupees would be the equivalent of just over 3 years. is barely enough to keep move. yes, family of 6 of of water a healthy diet has been beyond that means. but that is changing. we'll see, i know growth hubs and vegetables both for own families use. i'm to had boost her modest income of the same as as um, the name of the on some money selling would you please when they come back from the lansing. i sometimes send budgeted but as for 150 to 200 to be in the market. jacob spinet goes up to $450.00 to a piece per kilo. many own more. and when it's cheaper, i could motor tool and distribute it for free. the neighborhood is the manual with it the way that they work with the other youngsters. private vegetable gardens, the unusual around you move fiona lives in an informal settlement. next to the dumb space is extremely limited. but the non profit organization student has had to make it as the as the despite the difficulties

last year, reed, recalling that fateful night to dateline's dennis murphy, did you say i wonder if i hit him? i said, did i kill him? i said, could i have hit him? now? with reed's fate lying in the hands of a jury, anticipation building over a final verdict. so prosecutors have they offered a motive here? they don't have to under the law, but have they? well, prosecutors allege that reed and o'keefe that night were out at a local bar that they were drinking, that they got into a fight, that the relationship was falling apart amidst allegations of cheating. now reed, if convicted, faces up to life in prison as for turtle boy, you saw him mentioned in the story that pro reed, social media blogger well, he was arrested and charged with witness intimidation last year, charges that he denies. this is a very, very complicated case. lots of moving parts. that's captivating. paging dateline for that one. yeah, exactly. thank you erin. still ahead, the notebook star gena rowlands diagnosed with alzheimer's, the same disease her famous character battled. so what her family is sharing and how

. >> that is murphy dennis reporting another pair for nbc nightly news. >> they are known as serial killerscording to officials, there are at least 35 of them roaming the country now. >> and these two told police about one particular victim in colorado. >> they confessed to committing the murder of helene pruszynski. what was unique about them was that detectives often thought that there might have been another person may be in the car, waiting for whoever they took out into the field. that was one of the theories. >> so, these two guys that work together, these prolific serial killers, that certainly fit? >> it certainly fit. >> it's pretty seductive when a couple of serial killers were on the hook for a lot of other murders confessed in your murder, because it would close a lot of cases if you can link them to these guys. >> right. obviously, this is awesome. we got a confession. >> colorado investigators headed to texas to interview lucas themselves. the detectives showed him a map and asked him to pinpoint where he and tool picked up helene. >> and we took her way out in the country, we