In July, law enforcement announced that they had finally arrested a man suspected of being an infamous serial killer who once stalked Long Island. But what took them so long to catch him? Robert Kolker, who wrote a book about the case, examines the investigation’s stunning failures:

Since the case’s early days, law-enforcement officers have rarely spoken to the media. When I was reporting “Lost Girls,” my 2013 book about the case and victims, the police were largely silent. But after Heuermann’s arrest, some have been willing to discuss the investigation with a greater degree of detail and candor. Since July, I’ve conducted interviews with people close to the Gilgo case during every chapter of its bizarre 13-year timeline. (Several sources asked for anonymity, concerned that public statements by insiders might undercut the case against Heuermann before the trial.)

The story they tell—at times self-serving and at other times soul-searching—demonstrates, inadvertently and otherwise, how institutional rot helped contribute to the delays and paralysis of the investigation. What started out as indifference and apathy soon curdled into obstinance, willful ignorance and corruption. From the moment those women were found at Gilgo Beach, the law-enforcement culture of Suffolk County seemed so preternaturally ill suited to handle this case that a killer was allowed to roam free. Which was all the more galling, given what we know now—that everything the police needed to solve the case, they had almost on Day 1.