Nilsen began to spill out the details of his murders at once, despite being cautioned. His formal questioning began on February 11th. It lasted over thirty hours, spread throughout the week. Nilsen talked about his techniques and helped the police to identify parts of the victims. He did not really require much prompting. The information flooded out, as if to purge his conscience and get rid of every possible memory. He made no digressions and did not plead for compassion. He also exhibited no remorse. He claimed later that his professional training allowed him to feign calmness so the officials could take down the information. He told them what they would need for conviction, but nothing personal. Privately, he was afraid and deeply disturbed by what he had done.
Thanks to Nilsen, it was possible to find the various pieces of bodies and assemble them into a person, as they did with Stephen Sinclair. His lower half was in a bag in the bathroom. From there they could figure out which torso was his, along with the rest. With a definite identity, they were able to charge Nilsen and hold him pending further investigation.
Nilsen also accompanied police to 195 Melrose Avenue and pointed out where he had buried things and made bonfires.
A lawyer was now appointed to Nilsen named Ronald T. Moss, who listened with the police to Nilsen's detailed confession. He was satisfied that Nilsen understood what was happening.
When one police officer insisted that Nilsen was a predator, with malicious intent, Nilsen responded, "I seek company first, and hope everything will be all right."
Later he wrote his gruesome memoir for a young writer, Brian Masters, who turned Nilsen's ramblings into a book. As Master's says, "Nilsen is the first murderer to present an exhaustive archive measuring his own introspection. His prison journals are therefore a unique document in the history of criminal homicide."
After the confession, Nilsen was removed to Brixton Prison to await his trial. He was troubled by the reaction of the press that immediately followed his arrest. "No one wants to believe ever that I am just an ordinary man," he mused, "come to an extraordinary and overwhelming conclusion."