Transcript for Ronan Farrow describes how his Harvey Weinstein reporting unfolded: Part 1
Reporter: The biggest scandal in Hollywood in years. New outrage in the "Me too" movement. And I can't tell you I had a crystal ball. The fallout spreading from Hollywood to corporate America, the media and capitol hill. And knew there would be this incredible flood of people in industry after industry. Women and men coming forward with difficult claims. Senator Al Franken announcing he will resign. Pressure is going on president trump's supreme court nominee. Matt Lauer has been terminated from NBC news. Reporter: At the center of the saga that was the "Me too" movement there were the big names. Salma Hayek, Gwyneth paltrow, Ashley Judd. I thought no meant no. Reporter: Rose Mcgowan. A nightmare. And I will never be the same. You're about to hear from the reporter who obtained that secretly recorded audio. Reporter: And then there was Ronan farrow. Ronan was definitely underestimated by pretty much everybody, I believe. Reporter: A reporter and witness to a cultural shift that would define an era. Thousands joining marches and rallies. Reporter: It was a movement that swept the country. Demonstrating against harassment of women, demanding equality and change. Reporter: From the nation's capital to the red carpets of Hollywood. Why do you think you were able to get so many women to trust you? I was fortunate to come at this story at a cultural moment where brave sources were starting to come forward and chip away at the dam and where people were saying enough. Reporter: More than 80 women, according to the "New York Times," coming forward publicly with accusations against arguably the most powerful man in Hollywood, Harvey Weinstein. I thought he was a warthog from hell. I thought he was the single most ugly person I'd ever seen in my life. I was able to tell this story because people were brave as hell. And they are still being brave as hell and refusing to shut up. Reporter: Now in his new book "Catch and kill: Lies, spies, and a conspiracy to protect predators," Ronan farrow adds a new chapter to his reporting in the "Me too" era fch. "Catch and kill" is about systems and patterns of the abuse of power. Reporter: In the highly anticipated book Ronan writes in graphic detail an account of an alleged rape by former "Today" show anchor Matt Lauer. That portion leaked last week and immediately dominated headlines. There are not allegations of unfair. There are allegations of a Reporter: But in it he also claims NBC news mishandled accusations against lawyer. This is about what happens whenedia organizations enshrine in their corporate and legal practices a cover-up culture. A set of agreements and payouts designed to conceal abuse at a company. Reporter: Just this morning the president of NBC news fired off an e-mail to all staff with an opening line saying "Matt Lauer's actions were abhorrent." He goes on to say, "Ronan farrow's book takes than deniable fact and twists it into a lie, alleging we were a company with a lot of secrets. We have no secrets and nothing to hide." There is proof and a paper trail in this book. Just about everyone involved in all these transactions said this was explicitly designed to shut up women with allegations about sexual harassment. Reporter: It was early 2017. Harvey! Reporter: And movie mogul Harvey Weinstein was still living the high life. Appearing on red carpets at international film festivals and awards shows. When a cryptic series of tweets from former actress rose Mcgowan alluding to an alleged rape by Weinstein caught the attention of Ronan and his boss. When I released that tweet about why women don't report, that was my like okay, come find me, reporters, let's go. It was time. And that's exactly what happened. My plan worked. Now, Ronan for NBC comes to me very, very soon. There was a story that I was developing and I'd pitched about the Hollywood casting couch. Reporter: At the time Ronan was a fresh-faced reporter working for NBC news, a child prodigy who was accepted into Yale law school at just 15. But his on-air resume at that point was limited to a failed MSNBC show. Welcome to "Ronan farrow daily." Reporter: Canceled after just one season. I asked Ronan if he could be brave and he said yes. Reporter: When Ronan first reached out to rose she wasn't even naming Weinstein publicly. He turned to his sister for advice. I cared profoundly. My sister's experiences gave me insight into just how important the issue was. Reporter: Ronan is the son of Mia farrow and woody Allen. His sister Dylan has accused woody Allen of molesting her when she was just 7 years old. The drama first played out on tabloids in the early '90s but ultimately woody Allen was never charged with a crime. Certainly I never, ever abused my daughter. There was no sexual abuse that ever took place. My own sister was part of the history of women who came forward and refused to shut up even when people around them told them to. Even when you did. Even when I did. I let my sister down. I was one of those many people who our culture saying this is an albatross, this is inconvenient, why can't you just shut up? And thank god she didn't. I loved my father. I respected him. And that doesn't obviously take away from what he did. But it does make the betrayal and the hurt that much more I evolved from thinking she should shut up to understanding she was doing something important. That ultimately was inspiring to Reporter: In 2017 rose Mcgowan was on the cusp of going public with her story, and it was Ronan who was urging her to name names. Let's talk about how difficult it was to get rose Mcgowan to name Harvey Weinstein. Rose Mcgowan deserves a tremendous amount of credit for bringing forward her claim early. And this was a hard process. It was a gradual process. But by the time we were signature down on camera in early 2017 she was telling that story in shocking, painful detail. Reporter: Over the course of his reporting Ronan had started noticing strange things. Like a mysterious car that seemed to be following him. At what point did you say, wow, this is not just in my head, I'm really being followed? You start to see the same people behind you on the street and you're looking over your shoulder a lot and you're seeing a car parked outside your apartment at all hours. And people are starting to tell you you have to get a gun. Reporter: Ronan would eventually find out that Weinstein had hired blackcube, a firm largely run by former mossad agents, in an attempt to stop the publication of the allegations against him. This is the kind of stranger than fiction spy tactic that was not at all fiction. It was really happening. Reporter: Despite all the money and power that Weinstein wielded, it was the actions taken by some of his alleged victims like ambra Gutierrez that would ultimately help take him down. She had been shamed, and people underestimated her. They thought she's a lingerie model. And she had signed a million-dollar settlement that Harvey Weinstein and his attorneys felt confident would shut her up forever. Reporter: In a move that ultimately helped blow the story wide open, ambra had preserved a secret copy of a police recording of her and Weinstein. I'm feeling very uncomfortable right now. Please come in now and one minute. And if you want to leave when the guy comes -- Reporter: Weinstein was unaware ambra was wearing a police wire. Why yesterday you touch my Oh, please, I'm just used to that. You're used to that? Yes. Come in. But I'm not used to that. There had been a taped confession of Harvey Weinstein saying this is a pattern of behavior, I'm used to that. It was a game changer. Reporter: Even though no criminal charges from this were filed the recording was crucial for his reporting. What was your reaction as you I knew this was a story that had to be reported urgently. Having the tape kept me up at night. It meant that I had a moral obligation to get this evidence out before someone else got hurt. I'll never forget it. It was chilling. Reporter: Rich Mccue, Ronan's NBC producer at the time, also heard the tape. We played it for the head of the investigative unit. And his reaction confirmed our reactions. It was like man, if this thing airs he's toast. Reporter: With so much at stake Ronan got a safety deposit box at the bank of America right across from NBC's headquarters. I put all of my reporting material in there including this precious recording and I put that in that vault and wrote a note saying if anything happens to me you need to get this out and here are people you can contact to do it. Reporter: But then a setback. One of Ronan's strongest sources, rose Mcgowan, who had shared her story on the record, began to have second thoughts. Ultimately, I knew it wasn't NBC, it wasn't the right place. They wanted to put it on morning TV. I spiked that interview. It was me. My rape wasn't going to go with your cereal. I sent them a cease and desist. Reporter: Still seven months into their reporting Rhone sxn rich were comfortable they had enough to show the head of the news division Noah Oppenheim. Armed with a draft script and a plan for more reporting, they played him the recording from ambra. His reaction was incredibly jarring to me. It was almost like a deadpan reaction. It was other kind of people I've worked with in the news business who would have been practically ripping that audiotape out of my hands, or our hands, to air it that night. Reporter: In the book Oppenheim is quoted saying "I don't know what that proves. He's trying to get rid of her. People say a lot of things when they're trying to get rid of a girl like that. I'm not saying it's not gross but I'm still not sure it's news." When we left the meeting, Ronan and I were in the elevator and I turned to him and I was like something's up. That's not right. Reporter: By August 2017, in addition to ambra, Ronan says they had an accuser in shadow, anonymous corroborating witnesses, and they believed they could convince some accusers to agree to be named. But they say NBC executives told them to stand down completely. They issued a hard stop to reporting. They told me and a producer working with me that we could not take a single call with sources. Reporter: In a later memorandum to staff NBC news chairman Andy lack said after seven months without one victim or witness on the record he simply didn't have a story that met our standard for broadcast nor that of any major news organization. With NBC's permission Ronan would take his work to "The new Yorker" where he got more accusers to agree to be named on the record than he had at NBC his article was published on October 10th, 2017, just days after "New York Times" reporters Jody Kantor and Megan twoey broke the story of other Weinstein allegation ppz it was a watershed moment for the me too movement with even more victims feeling empowered to break their silence. Any comment, Harvey? Reporter: Weinstein was arrested in 2018 and now awaits a January trial on charges of sexual assault and rape related to two women. He has pled not guilty those charges and has consistently denied any allegations of non-consensual sex with anyone. Harvey Weinstein told ABC news "What Ronan farrow insinuates as factual accounts are actually an amalgamation of unrelated pieces of information that he formed together to tell what is little more than a dramatic fictional tale." It is a huge story and an important one in a way that was bigger than Harvey Weinstein, that was about vast systems that we are still struggling to Matt Lauer, the long-time host of the "Today" show, has been fired. Reporter: Coming up, new details about Matt Lauer's firing and questions about NBC's reason for passing on Ronan's Weinstein story. Is it your belief today that their explanation for wanting you to put a pause on the story was because they were concerned that Weinstein had information about Matt Lauer? Stay with us.
This transcript has been automatically generated and may not be 100% accurate.