The third victim of the knife-wielding maniac who left a bloody trail across Manhattan in a broad-daylight stabbing spree Monday has died of her injuries as the brute confessed to the random killings and was slapped with murder charges, police and sources said.

Wilma Augustin, 36 — the alleged third and final victim of 51-year-old Ramon Rivera — succumbed to her injuries in the hospital Monday evening, police said. 

Rivera, a homeless man with an extensive criminal record and reported mental health ailments, allegedly confessed to the unprovoked stabbings that began in the morning and crossed the width of the borough from Chelsea to the East River, sources told The Post.

A 36-year-old male construction worker waiting to be picked up from work and a 67-year-old man who was fishing in the East River were also killed in separate stabbings throughout Manhattan by the same suspect, police said.

Rivera, who was released from Rikers a month ago and was living at Bellevue Men’s Shelter, was charged with three counts of murder, police announced shortly after 9 p.m.

He walked with his head down and didn’t respond to reporters’ questions as he was led out of Manhattan’s 10th Precinct in a white jumpsuit, handcuffs and ankle shackles Monday night. The accused killer stared icily at the crowd of reporters and onlookers once he was seated in the back of an unmarked squad car. 

Police officials called the killings random and unprovoked. 

“As of right now, these attacks seem to be unprovoked, that he just walked up to them and began to attack them with the knives,” NYPD Chief of Detectives Joe Kenny said at a morning news conference. 

His chilling murder spree began around 8:20 a.m. when he walked up to the construction worker, Angel Lata Landi of Peekskill, and plunged a knife into his stomach in front of 444 W. 19th St. in Chelsea and ran off, police said. 

About two hours later, Rivera reappeared near the FDR Drive at 500 E. 30th St., where he allegedly attacked the fisherman, according to cops. 

He fled north toward East 42nd Street and First Avenue, where he allegedly knifed Augustin about a half-hour later in the shadow of the United Nations building as terrified bystanders rushed to help. 

Landi and the 67-year-old victim were rushed to Bellevue Hospital, where they were each pronounced dead. Augustin was brought to Weill Cornell Medical Center, where she was later declared dead as well. 

The identity of the oldest victim was withheld by police pending family notification. 

Several good Samaritans helped police capture the violent madman. A British tourist and UN Diplomatic Security Service special agents helped track down the suspect while a cab driver followed him and alerted a nearby NYPD officer, Robert Garvey, who ultimately cuffed Rivera and stopped him from additional senseless stabbings. 

“If Officer Garvey was not there, these random acts of violence, this person conceivably would have continued those random acts of violence,” Mayor Eric Adams said at the press conference. “So he saved the lives of fellow New Yorkers.”

Police recovered two bloody kitchen knives believed to have been used by Rivera.

The alleged killer has been arrested for burglary, assault and grand larceny over the past year and has had two mental health episodes in which police responded, sources said. 

It’s not clear why Rivera was back on the streets, Adams said. 

“There’s some real questions that we need to look at on why he was on the street, and he has some severe mental health issues that should have been examined, and that’s what we’re looking to spot in the investigation,” the mayor said.

Additional reporting by Dorian Geiger