A Manhattan man accused of fatally stabbing his elderly wife was caught after phoning his niece and telling her he had done “something bad,” prosecutors said Sunday.

Cops arrived at the scene at West 144th Street to find suspect Geraldo Balbuena, 68, holding a “large wood-handled knife” — and his 79-year-old wife’s body lying in a pool of blood nearby, court papers said.

Officers had been brought to the home after Balbuena’s niece phoned 911 telling an operator that her uncle told her he’d done a “bad” thing and that he was suicidal, the document said.

Arriving police observed the alleged wife-killer through his fire-escape window standing in the apartment holding the knife, according to the official complaint against him in Manhattan Criminal Court.

Upon entering the apartment, cops found Balbuena’s wife, Lanilda Nuez, “lying unresponsive on the bedroom floor in a pool of blood,” the court docs said.

Lanilda was pronounced dead at St. Luke’s Hospital at 11:15 p.m. after 35 minutes of CPR, prosecutors said — less than an hour after police arrived at the scene.

Balbuena, 68, faces charges of second-degree murder and fourth-degree criminal weapons possession.

Neighbors on Saturday told The Post that the pair may have been feuding over a house they owned.

Balbuena had been drinking and handing out beers to adults and candy to children on the day of the murder and also spoke to neighbors about committing suicide.

Friends and family said Lanilda, affectionately known as “China,” was a breast-cancer survivor who often held court from her stoop.

“She was everyone’s grandmother on this block. She was funny. She was feisty, that’s why everyone loved her. She was always making everyone laugh,” said her granddaughter, Chanill Arashiro, 30.