[ cheers and applause ] this is "nightline." >> tonight, more powerful than morphine and heroin -- fentanyl, it killed prince and it's taking lives and destroying families across the nation. >> my son died from fentanyl, 100% fentanyl. >> the dea's urgent warning that saying that even exposure to fentanyl can kill. plus, heart-wrenching words we leased today from the mother of former stanford swimmer sentenced to just six months in jail for sexual assault. and new details about that night as public pressure mounts for the judge in the case to step down. and the greatest goodbye. we were in louisville, kentucky, tonight, where thousands lined the streets to bid their final farewell to muhammad ali, as one of america's most inspirational

sports legends, soars on his own wings, through the hearts of his fans. but first the "nightline" five. number one is just

♪ good evening, thank you for joining us. we're coming to you tonight from louisville, kentucky, the beloved hometown of muhammad ali. he was laid to rest today as

thousands of mourners celebrated one of america's greatest sports legends. we'll have more on that later in the broadcast. but first, we begin with the growing epidemic that's killing americans in record numbers. a painkiller significantly more powerful than heroin -- fentanyl. the dea issuing an urgent warning. now we take an in-depth look. >> reporter: fentanyl, the drug deadlier than heroin. causing an epidemic of overdose deaths all across the country. today the dea issued a warning. >> i want to take a minute today to talk to you about something very important. it could kill you. that's fentanyl. >> reporter: even touching a few amounts, like a few grains of salt, can be lethal. it's the substance connected to the sudden death of pop icon prince ♪ this is what it sounds like when the doves cry ♪ >> reporter: songs like "when doves cry" the soundtrack to a generation. last week, the midwest medical

examiner's office determined that prince died of an accidental prescription drug overdose. self-administered fentanyl. >> at paisley park, person down, not breathing. >> reporter: it's a synthetic opioid, 80 to 100 times stronger than morphine. 20 to 40 time more potent than her aoin heroin. >> he was prescribed an amount and took it all down slenl, or perhaps he was getting it from other people, or perhaps he was getting it from the street. >> reporter: the rise of this dangerous drug investigated in a fusion documentary "death by fentanyl." >> here in massachusetts, we are losing four or five people a day. they are dying from this epidemic. those are big numbers for a state like ours. >> reporter: for communities and families that have been battling the opioid epidemic, fentanyl is a frighten derm and crisis that

has already killed so many. >> i had three babies in three years. >> brave woman. >> reporter: a family of five living in the quiet suburb of middleborough, massachusetts. james, the youngest son, and patrick, the oldest, both got hooked on prescription pills. and then heroin. in 2013, james, just 26 years old, died of a heroin overdose. >> when i lost james, a big piece of me, you know, died with him. >> reporter: soon after, his brother james passed away, patrick decided to get clean. in the summer of 2015, he celebrated a year sober and was putting his life back together. >> we had my wedding and i asked him to be my best man. >> on the night of the wedding, i took his beautiful face, he was beautiful man, and i put it -- and i said, i'm so happy, you've given me the best gift of the past year, of recovery. >> when he brought her home, i was really happy.

>> the day i left for my honey moon, he text me and said, he was so proud to be there with me. and then i got the phone call. >> that he died tonight. he said, no. i said, he did, honey, he died tonight. >> his roommate found him dead in his room with a spoon and the needles next to him. >> reporter: patrick died just three days after his brother's wedding in his apartment in new hampshire. >> i received a call from the medical examiner's office. he told me my son died from fentanyl. 100% fentanyl. i said, are you telling me there was no heroin in there? and he said, not a drop. 100% pure fentanyl. >> a lot of people would say, what's the difference? it's an overdose. what's the difference? but for you, there's a big difference. what is it? >> yeah, there is a big difference. because heroin may kill. fentanyl will kill. >> reporter: they believe patrick might have thought he

was buying heroin, but was sold fentanyl instead. >> unfortunately, it's being sold as heroin on the streets and that's one of the sources of all the overdoses because fentanyl is so powerful. >> reporter: at the meridian house, an addiction recovery program in boston, nearly everyone has stories of overdosing. fentanyl has made the odds more likely. >> you can't get just heroin without any trace or touch of fentanyl, i think around here. >> david herric has been an addict since he was a teenager. >> there's no ingredients on the bags. fentanyl gets in there and the little guy has the big punch and takes you out. >> reporter: as fentanyl became more available, an enormous black market opened up. >> you have the patch, the spray, the lollipop. but you also have the street fentanyl which is sold in little bags, much like heroin. >> it's like a name brand cereal, and not name brand cereal. >> reporter: david says his

first encounter with fentanyl was with prescription patches. >> i would microwave it to get it soft, suck it up in my needle and put it in my arm. just a little water added, it's the purest form. i'm getting it not from a dealer. i'm getting it from the person it was prescribed to. >> reporter: but after too many near death experiences, david says, he finally wanted to get clean. >> i think it's wiping people out in an alarming rate. a lot of addicts are dying left and right. something finally clicked where it was like, a-ha, what do i have to do to get away from this stuff? >> reporter: according to the d.a., the vast majority of fentanyl comes from over the bord border. we've just arrived in mexico. they've asked us not to say the location. we traveled to sinaloa to get an

up-close operation at a fentanyl operation, one that puts money straight into the cartel's pockets. he covered his face. javier has asked us to obscure his face and distort his voice. he tells us, he and his family have been in the drug trade for generations. [ speaking spanish ] >> the nickname is the little devil, because it's so dangerous that they have to handle with it a lot of care. is it difficult to make fentanyl? [ speaking foreign language ] >> reporter: growing poppies to make heroin can be risky and time consuming. fentanyl, however, is purely synthetic and therefore, cheaper and faster to produce. they test the concoction by heating it up. javier says if it's not good

quality, it would burn. from the streets of mexico, fentanyl is making it into the homes of americans like the avitavolis, still grieving the tragic loss of their beloved son. >> they took him from us. i know it sounds weird, but in a world that people don't understand what going on out there, it changes everything. because my boy might be alive toda today. next, new details emerging about the stanford university sexual assault case, and what the judge heard before sentencing brock turner. and the emotional final farewell to the greatest, right here in louisville tonight. ♪

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♪ it's a case that even the vice president has weighed in on, that stanford university sexual assault sparked a reaction and growing outrage on all side. now new details about that fateful night in the plea the mother made to the judge for her son. now under fire for what has widely been criticized as a lenient sentence. >> reporter: tonight new documents in the stanford sexual assault case, whereim swimmer brock turner was convicted of sexually assaulting a woman who lay unconscious behind a dump story, casting new light on the multiple lives shattered that night. the sister, writing to the judge, is that the damage you inflicted is irreversible.

she said she was at the party that night with her sister and the initial police report said he was weird, aggressive. but there was another family in this case, brock turner's. today we're finding out the words his mother wrote to the judge who would decide her son's sentence. >> i know what a broken heart that feels like, it's a physical pain that starts just below the collarbone and extends just below the rib cage. it's a crushing and heavy ache. this verdict has destroyed us. and her prophetic message of fear that he would be a target. a stanford boy, collegiate athlete. all the publicity would be a death sentence. today, swimming banned him for life. >> i think what this case is making everyone think about is, you know, boys from nice families, from dayton, ohio, can do these things, and what are we going to do about that?

>> not mentioned once in his mother's letter, the victim. >> reporter: has he ever apologized? >> he has not apologized for sexually assaulting her. >> reporter: has he ever taken responsibility for this? >> he's apologized for drinking and made some apologies for how she feels. >> reporter: turner insisted throughout his defense that the victim consented to the encounter. turner was sentenced to six months in jail, but will serve only three. when he gets out in early september, he'll have to register as a sex offender. as his mother says in her level, on the same level as a pedophile, child molester. given what you know about him now, are you concerned he might do something like this again? >> you know, i don't know. i think that these types of crimes require registration, because we know that there are repeat offenses usually. >> reporter: the documents released show how much alcohol had to do with the tragedy.

brock turner telling police he had about seven cans of beer and some whiskey. while he wasn't blacked out as the victim reportedly was, he said he never got her name and probably would not be able to recognize the vim if she saw her again. coral frederick and peter johnson were riding their bikes and stopped when they saw two people on the ground near a dumpster. >> she wasn't moving. >> reporter: and the man on top of her was? >> yeah. my friend said, what the [ bleep ] are you doing? he later said, i didn't do anything, when he was laying down on the ground. tried to make like nothing happened, essentially. >> reporter: when turner made a run for it, he and johnson ran after him, pinning him to the ground. >> we helped restrain him until the police came. >> reporter: when you saw her on the ground, was it pretty obvious was what happened? >> yeah. she was half naked, so, yeah. >> reporter: after the sentencing, the judge who gave that six-month sentence is coming under fire. >> the judge is saying it

doesn't matter what your past actions were, just don't do it again. >> i don't think six months is nearly enough. >> a petition to remove the judge with a million signatures was delivered to the courthouse today. >> i think that's an appropriate action in this case. the judge has failed to live up to his duty says as a member of the california judiciary. >> reporter: and some jurors refusing to serve in his courtroom. a public defender says per ske and his family have received threats over the phone. >> reporter: can you give me a sense of what is being said in these calls? >> they're threatening, they use a lot of profanity. they hope that he dies, they hope his kids get raped. >> reporter: since last week, the victim's impact alert has gotten over 15 million views on buzzfeed alone. >> we just don't hear these kinds of accounts from survivors. >> reporter: the actresses from hbo's "girls" releasing this psa dedicated to the survivor in the stanford case. >> she is someone.

>> she is someone. >> reporter: even the vice president drawn in, joe biden writing his own letter, saying, i do not know your name, but your words are forever seared on my soul. those are words that have stoked national outrage, as biden put it, about our college campuses, where 1 in 5 women is sexually assaulted. for "nightline," i'm matt gutman in los angeles. and next, the crowds, the procession, the heart felt tributes and the words of inspiration, as america bids a heart felt goodbye to one of his most powerful sports legends. abc news "nightline," brought to you by the lincoln motor company. ♪ ♪but i'm not gonna let 'em catch me, no no,♪ ♪not gonna let 'em catch the midnight rider,♪ ♪yeaaahh...

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♪ >> and finally tonight, we're here in louisville where hometown and the nation said goodbye to the greatest. >> this is cassius marcellus clay. he's young, he's handsome. >> they know it. >> and many people believe he'll be the next heavyweight champion of the world. >> reporter: he brought the world to its feet and his

opponents to their knees with his quick lands and punishing blows. >> if he goes back, he'll end up in a ringside seat. >> ali, ali! >> reporter: and today, people by the thousands poured into the streets of louisville to pay homage to the icon, the champion, the legend, muhammad ali. >> float like a butterfly and sting like a bee. >> reporter: as an upand coming boxer in the seg grated south, he was a powerful inspiration. idolized by young fans who saw his triumph as their own. as his hearse carried him through his hometown streets for the last time, a new generation of fans ran alongside him, possessed by the same adoration. his pallbearers, the hollywood star that immortalized ali's life in film, will smith, mike tyson and lennox lewis, heavyweights that followed in

his foot steps. ali memorialized inside louisvil louisville's largest arena. >> muhammad ali said, i'm proud, i'm pretty, i'm glad of who i am. that infused in africans a sense of somebodiness. >> reporter: an international force inside the ring and out of it. >> he stunned the world when he secured the release of 15 hostages from iraq. [ applause ] as his voice grew softer, his message took on greater meaning. when he lit a torch that seemed to create new light in the 1996 olympics. >> by god, he was gonna make those last few steps, no matter what it took. the flame would be lit, the fight would be won, the spirit would be affirmed. >> reporter: remembered as a loving husband, father. >> we love you so much, daddy. until we meet again, fly,

butterfly. >> reporter: but above all, as an unyielding force for good. the greatest there ever was. >> today, this outpouring of love and respect proves that 35 years after he stopped fighting, he is still the champion of the world. [ applause ] >> i must be the greatest. i'm a bad man. i shook up the world! i shook up the world! >> years ago when another great fighter died, a sports writer wrote, joe lewis was a credit to his race -- the human race. tonight those words ring true of the great muhammad ali. thank you for watching abc news. tune in for "good morning america" tomorrow and as always, we're online on our facebook page and on abc news.com. goodnight, america, have a good weekend.