Santos was taken into police custody early Saturday. Police say he has been arrested at least a half-dozen other times in the past two years, three times on assault charges. It wasn't clear whether he had a lawyer to speak for him.
The victims, all men, were attacked as they slept in doorways and sidewalks in three different locations in Chinatown, which is packed during daylight hours but empties out at night.
Police responded to a 911 call just before 2am as one assault was in progress. They found one man dead in the street and a second with critical head injuries.
A search of the neighbourhood turned up three additional bodies.
The New York Post published photos of two of the victims under white sheets, one slumped in a blood-spattered doorway, the other on the sidewalk. The identities of the victims have not been released.
Two of the men were killed on The Bowery, which cuts through the heart of Chinatown and has for decades been known as New York's skid row. Two more died on East Broadway, the neighbourhood's main street.
The lone known survivor was hospitalised in critical condition. Police planned to interview him as soon as possible, Baldassano said.
Another homeless man who had slept in the area, Stephen Miller, said he knew one of the victims as kind and quiet.
"No one knew him by name, but we saw him every day," Miller said. "At this point, I'm just sad. This guy never did anything. Just had a life to live. It sucks that he's out here in the rain and everything, but it doesn't mean he doesn't have a life to live."
New York City's homeless population has grown to record levels over the past decade, and the homeless remain among the most vulnerable residents. In the past five years, an average of seven have been slain each year.
Mayor Bill de Blasio launched new homeless outreach efforts early in his tenure in an attempt to move more people off the street and into shelters, but the programme has faced challenges. City efforts to build more homeless shelters have dragged due to neighbourhood opposition.
De Blasio tweeted Saturday that he's "stunned and horrified by this senseless act of violence against the most vulnerable members of our community."
The attacks happened in one of the few downtown Manhattan areas that has retained its character as a centre for new immigrants, through gentrification has started to creep in lately.
During the day, it bustles with small shops, restaurants and markets doing business in Chinese, as a mix of residents and tourists pack the sidewalks. At night it can be desolate in some sections.
- AP
