this is "nightline." >> tonight, genealogy justice? an 8-year-old girl abducted and murdered. the killer taunting police for decades. after 30 years, the cold case now breaking open thanks to a new cutting-edge dna tool. >> we were able to use genetic genealogy to narrow it down to two brothers. >> the new scientific advancement that's making it harder to get away with murder. plus a volcano sightseeing tour boat blasted by an eruption. [ screaming ] a lava rock crashing into the ship. >> it landed a person. and it was so glowing when it was on the ground. >> survivors telling their stories. >> i just was kind of like, oh my god, i got to get to my kid.

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good evening. tonight an incredible development? a decades-old murder case thanks to a new tool in dna analysis that could be the key to solving many other crimes like this.

investigators are now combining genealogy with dna samples to track town a potential suspect's family. a technique that is revolutionizing forensic science. abc's wit johnson is on the story. >> the fbi now has a more detailed description of the suspected killer -- >> this guy is a monster, he's a coward. >> reporter: it's the unthink about crime that haunted ft. wayne, indiana, for three decades. >> a big break in a decades-old cold case -- >> reporter: until a clue hid no one genetic code landed a suspected child murderer behind bars. >> the abduction and death of 8-year-old april chinsly has haunted this community for over 30 years -- >> reporter: the arrest part of a new wave of crimesolving,gynk. to hunt the most violent offenders. 1988, a killer on the loose. taunting police, threatening to strike again. the face of an innocent young girl thrust into the national

spotlight, 8-year-old april tinsley, going to play at a friend's house, never making it home. little april kidnapped, raped, and strangled. her body dumped in a ditch. >> i think about april often. i carried her picture in my wallet for a long, long time. >> reporter: the case baffling authorities. the mysterious killer inflicting more fear. leaving rambling, misspelled messages, authorities say, like this carving on a barn door two years after the murder. "i kill 8-year-old april, i will kill again." then in 2004, according to police, more notes left at the homes of other young girls reading, "hi, honey, i've been watching you, you are my next victim." >> how chilling are the details of this case? >> i can assure you that anyone who worked on this case has been haunted by it. >> reporter: investigators say dna from some of those notes match dna found at the crime

scene, with a madman nowhere to be found. police putting out this composite sketch based on his dna profile. >> i was part of this investigation when it started. and there has not been a day, a month, or a year that has gone by without someone in this room working on this case. >> reporter: but for decades, nothing. >> there's got to be a bright spot. it's going to come someday. and then there's moments you have, like, this is never going to be solved. >> reporter: then on sunday, a stunning development. >> 30 years. 30 years this family has waited for answers. and on sunday, we were able to give them some of those answers. >> reporter: police taking 59-year-old john d. miller into custody at this mobile home park where he lived. about six miles from where april's body was found. >> i know he had a bad temper, always be cussing and swearing, throwinging stuff. >> reporter: investigators say

they asked miller if he knew why he was being questioned. his response? "april tinsley." then, according to police, a confession. how critical is that confession in the case? >> the dna is still going to be the most important piece of evidence in this case. you combine that with the confession, and it's hard to figure out exactly what his defense is going to be. >> today is a big win for law enforcement. and this investigation illustrates the dogged determine nation of the investigators who never wavered, never gave up, and kept moving forward for the last 30 years. >> i can't tell you how happy i am for janet. she finally has some closure to this. i know it's still going to haunt her the rest of her life, every day. but i am so happy that she can finally rest a little bit, knowing that he is finally caught. >> reporter: the break, police say, thanks to a new cutting-edge tool combining the power of dna, genealogy, and the internet. creating a genetic profile from crime scene dna, authorities say

they uploaded it to a public database called ged match, leading police to identify relatives and zeroing in on a suspected killer. john miller. investigators later recovering a dna sample from miller's trash. that, they say, tied him to april's murder. is there any concern about the legality of that? digging through somebody's trash? >> the supreme court specifically ruled on, can police use evidence that they find in someone's garbage? and the answer is, typically, yes. if you're discarding your garbage outside of your home, you're pretty much giving up an expectation of privacy associated with that trash. >> this is the fifth case that has been announced in which we were able to help investigators determine who the suspect is. >> reporter: genetic genealogist cici moore made a name connecting families to long-lost relatives. >> the power of geneti geneti g

reunite families, it's just as powerful for law enforcement. >> reporter: she's working with a lab in virginia and law enforcement attempting to solve the most challenging cold cases like the tinsley murder. >> we were able to use genetic genealogy to narrow it down to two brothers. once we get to that point, we turn it over to law enforcement and they have to investigate those brothers and determine which one is most likely the suspect. >> reporter: john miller's brother, who did not want to be shown on camera, says he too was interrogated by police. >> they questioned me about an hour and a half. plus they took my dna. >> reporter: he now says he wants nothing to do with his brother. >> as far as i'm concerned, when they told me that he confessed to this crime -- my brother died. i'm done. >> reporter: the murder of little april tinsley, just the latest in a series of high-profile cases.

cracked, investigators say, using the same cut exampling-edge technique. >> the new dna technology is just a wonderful thing. >> reporter: the first to make worldwide headlines, the so-called golden state killer, an elusive criminal whose reign '70s and '80s police say included threatening phone calls to his victims. but in april, investigators say that ged match website helped lead to the arrest of 72-year-old joseph deangelo, the former police officer now charged with a dozen murders, suspected of committing more than 50 rapes. and just last month, according to police, dna left on a restaurant napkin busting open the 1986 unsolved murder of 12-year-old michelle welch, officers arresting 66-year-old gary hartman. what's pleaded not guilty. >> today we're at a point where

if you're a criminal and you've left your dna at the scene, you might as well turn yourself in now. >> reporter: then days later, across the country in pennsylvania, a popular deejay arrested in a 25-year-old cold case. the murder of teacher christie morack in 1992. investigators using genetic genealogy to track 49-year-old raymond rowe, lifting a dna sample from his water bottle and chewing gum, then charged with homicide. law enforcement agencies across the country are now hoping to use the new technology to solve their cases. >> my work has always revolved around families. and trying to help provide closure. >> reporter: for the families of those murder victims, fresh hope following decades of unanswered questions. >> somewhere up there there's a little girl dancing with her angels. she's celebrating. so when you get on your knees tonight and talk to her in your dreams and prayers, tell her. they did it. they did it and we got him.

>> reporter: for "nightline," i'm wit johnson. next here, a lava bomb strikes a tour boat in hawaii. passengers telling their terrifying tales of survival. what about him? let's do it. ♪ come on. this summer, add a new member to the family. at the mercedes-benz summer event. lease the glc300 for $429 a month at your local mercedes-benz dealer. mercedes-benz. the best or nothing. touch shows how we really feel. but does psoriasis ever get in the way? embrace the chance of 100% clear skin with taltz. up to 90% of those with moderate to severe psoriasis had a significant improvement of their psoriasis plaques. most people were still clearer after one year.

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did theyet too close? "nightline" welcomes abc's will carr. [ screaming ] >> it was coming and there was nowhere you could go. >> reporter: watch this terrifying moment. molten rock, ash, and debris exploding hundreds of feet into the air off the coast of hawaii's big island. in the crosshairs this lava tour sightseeing boat, packing over 50 passengers and crew. video capturing the chaotic scene when a lava bomb, a massive chunk of flaming rock, shot out of the ocean where lava has been pouring from the nearby erupting kilauea volcano. >> it crashed through the roof and it landed on a person. and it landed on the floor. and it was still glowing when it

was on the ground. >> reporter: dr. lee and his wife donna sprang into action while debris continued to fall from the sky. >> i started game planning in my mind. the life vests, who can swim if we go over, how do we keep ourselves from the shore? my kids were separated from me, so i just was kind of like, oh my god, i got to get to my kids. >> reporter: lava rock striking one woman in the leg, fracturing her femur. the li family coming to her aid. >> we just sort of stabilized her hip with life preservers, covered her so she wasn't going into shock. >> where would this compare with what you've seen over tca >> i've seen a lot of things. this was just crazy. >> reporter: the li family ing lucky they endured burns and scrapes, but everyone walking away. >> i thought for a moment that was it. this is how it's going to go.

and it was -- it was a terrifying moment. >> reporter: since may 3rd the kilauea volcano has erupted continuously, ravaging the landscape of hawaii's big island. >> the ongoing flow from these fissures creating these huge fields of now-hardened lava. some places it is stacked 20 feet high. >> those roars are steam and gas flying out of these vents. that stuff is 2,000 degrees. >> reporter: my colleague, matt gat minute, getting a close-up look during the early explosi explosions. >> there are multiple times more sulfur dioxide in the air now than a couple of days ago, pumped into the air by that massive cauldron of lava behind me. >> reporter: giving us a birdseye view at the height of that liquid rock devouring everything in its path. is we can fly it's over those two rivers of lawyer have a down there. you can actually feel the heat being generated from 2,000 feet above them. >> reporter: nearly two months of unstoppable lava flow

destroying hundreds of buildings and permanently covering miles of lush greenery in a coat of gray ash. the. geological survey estimating the lava flow has added 690 acres of new land to the big island. today we went inside the evacuation zone with the hawaii national guard. >> in the immediate area, there are present hazards. sulfur dioxide, can shift with the wind. and a certain part per mill, you can feel it and feel hurt. >> reporter: here a place people once called home. now a flowing stream of magma. in the distance you can see that hellish orange glow. that is a river of lava. the rapids flowing over what used to be a community, hundreds of homes destroyed. you can see that lava rock has cut off this road. since the beginning of may it has been raining molten rock like this across the area, for miles, and at this point there's no end in sight.

kilauea is one of the world's most to have volcanos, spewing since 1983. for decades tourists have flocked here to witness nature at its best and its worst. last year alone, 2 million tourists visited hawaii volcanos national park. >> the lava lake would create a really magnificent glow in the evening. because this is the legendary home of pele, the volcano goddess, there's such a sacredness to this area that people i think really walk away with that. >> reporter: but the recent eruptions have been massive even for a community accustomed to volcanic activity. large swaths of the area have been cordoned off for safety so tourists have been taking in the sights from the sea. but monday the danger came to them. boats operating in the area now instructed to keep a distance of 300 meters from the explosion site. [ screaming ] tonight the coast guard trying to figure out if the boat

captain went inside a safety zone, potentially endangering lives. dawn li momentarily still holding the rock that burned her back, choosing to cast aside questions about the captain's decision. >> i'd like to thank him for getting us out of there as expeditiously and safely as he did. and not to cast stones. but that we're just all so thankful to be alive. i think he did his job. >> reporter: for "nightline" i'm will carr in hilo, hawaii. next here, she was an unknown entering the boston marathon on a whim. then she shocked the world. cr ibe discover our largest variety of crab and crab dishes all year! like new crabfest combo. your one chance to have new jumbo snow crab with tender dungeness crab. or try crab lover's dream. sweet, juicy king crab and jumbo snow crab

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as we prepare to honor some of the world's most famous athletes at the espe awards, tonight we're going to celebrate a little-known marathon runner who became a breakout star after a recent performance in boston. >> this will be the second-place finer, sellers --

>> reporter: the windchill around freezing when sarah sellers crossed the finish line at the 2018 boston marathon. it was clear the then-26 year old from arizona had no idea what she'd accomplished. >> when i crossed the iesyad n e ldavd ten. i was haen it wasn't until i asked the officials and they repeated over and over that i was second place, at that point it was like, is this some crazy dream? >> reporter: sellers a high school and college superstar, until an injury forced her off the track. >> my junior year i think i had the third best time in the country among collegiate women for the 10k, so i was competing at a high level. to have what i thought was a career-ending injury -- i never thought at that point that i would get back to competing at a high level again. >> reporter: virtually unknown heading into boston, now sarah is being recognized with an honorary espy for her achievements at the boston marathon. >> even during the race i kept

having to remind myself, i'm feeling the wind and the rain, feeling discomfort, so it must be real. but almost three months out, it's interesting to look back and think about how insane that seemed at the time. >> reporter: also a full-time nurse, anesthetist in tucson, sellers says her day to day has given her perspective away from the road. >> being a nurse anesthetist, i see what patients and families go through every day. it really gives a lot of meaning and perspective to realize that i love this sport. but there's a lot bigger things out there, and just competing is a privilege. >> reporter: but now after that surprise performance in boston, he's setting biggeralincluding >> it's going wo to consistently compete at a high level. but i think boston has given me the confidence that i belong up there and that i can compete with those women. >> richly deserved, our

congratulations to her. and you can watch the 2018 espy awards hosted by danica patrick tomorrow at 8/7 central right here on abc. thank you for watching "nightline" tonight. as always, we're online 24/7 on our "nightline" facebook page. thank you again for watching and good night.