Yesterday on “The Daily,” we heard about the government’s failure to crack down on the explosive growth of child sexual abuse imagery online. In the second half of this series, we look at the role of the nation’s biggest tech companies, and why — despite pleas from victims — the illicit images remain online. Guest: Michael H. Keller, an investigative reporter at the The New York Times, and Gabriel J.X. Dance, an investigations editor for The Times, spoke with the mother and stepfather of a teenager who was sexually abused as a child. For more information on today’s episode, visit nytimes.com/thedaily. Background reading: The tech industry has recently been more diligent in identifying online child sexual abuse imagery, but it has consistently failed to shut it down, a Times investigation found. Facebook accounted for more than 85 percent of the imagery flagged by tech companies last year.Two sisters opened up about their lives after being sexually abused as children. Photos and videos of them online continue to remind them of the horrors they experienced.Here’s the first episode in this two-part series, describing how a finding from a tipster led to The Times’s monthslong investigation of online child abuse imagery.