Exclusive | Suspected NYC stabber — who killed 3 in chilling spree –

The alleged spree killer who fatally stabbed three people in Manhattan told cops in a chilling confession that he targeted his innocent victims because they were “alone” and “distracted,” sources told The Post Tuesday.

Ramon Rivera, 51, spent hours sleeping in police custody after he was nabbed in Monday’s bloody broad daylight stabbing spree, sources familiar with his arrest said.

When he awoke, he waived his Miranda rights and allegedly – and calmly – gave a full confession, sources said.

Rivera, a homeless man with mental health problems and an extensive criminal record, according to sources, was awaiting arraignment Tuesday on three counts of first-degree serial murder.

The “unprovoked” random attacks unfolded over the course of two hours, beginning with the stabbing of a 36-year-old male construction worker waiting to be picked up from work in Chelsea, police said.

The deranged stabber – Rivera, police said – then trekked across Manhattan to the East River waterline, where he fatally knifed a 67-year-old man who was fishing, cops said.

A third victim – Wilma Augustin, 36 – was stabbed near the United Nations building, police said. She was rushed to a nearby hospital, but succumbed to her injuries hours later, according to cops.