In one robbery, the perpetrators smeared white powder laced with fentanyl under the victim’s nose. In another, they offered someone marijuana laced with the drug and waited for the person to fall unconscious, the police said.

Kenwood Allen, 34, and Sean Shirley, 36, kept their campaign of robberies in Lower Manhattan nightlife districts brutal and simple, the police said — they targeted people in bars who looked like they had money, waited until the patrons came stumbling out, then threw them up against a wall to take whatever they had.

“They bumrushed them,” James Essig, chief of detectives at the New York Police Department, said Thursday.

Between March and December, 2022, Mr. Allen and Mr. Shirley committed 26 robberies and attempted robberies, using drugs to subdue their victims, the police said. Five people died from the overdoses, including four in just 15 days, prosecutors with the Manhattan district attorney’s office said this week. Among them, the police said, was Kathryn Marie Gallagher, 35, a fashion designer whose pieces had been worn by Lady Gaga, the actress Laverne Cox and dancers of the New York City Ballet.

Mr. Allen was indicted in December in the overdose deaths of Nurbo Shera and Ardijan Berisha. On Wednesday, he was charged with the killings of Ms. Gallagher, Alexander Rudnitsky, a 25-year-old student at Rutgers University who lived in Yonkers, N.Y., and Sadath Ahmed, 33, who lived in Queens.

Mr. Allen has been charged with 10 counts of second-degree murder — two for each of the five deaths. One charge accuses him of acting with depraved indifference to human life, the other of acting in furtherance of another crime. He was also charged with 17 counts of robbery and attempted robbery. He pleaded not guilty at his arraignment on Wednesday.

Mr. Shirley is charged in the overdose deaths of Mr. Ahmed and Mr. Rudnitsky. He was arraigned on Thursday afternoon, pleading not guilty to charges of second-degree murder, robbery, and grand larceny.

The indictment described a series of texts about money between him and Mr. Allen. In court, Brian Rodkey, an assistant district attorney in Manhattan, said Mr. Shirley and Mr. Allen drugged the victims, “robbed them, and left them on the street, not caring whether they lived or died.”

Mr. Rudnitsky was found on a street in the Bronx on the early morning of July 22. He was unconscious and rushed to a hospital where he was declared brain-dead, according to his older sister. He was taken off ventilators about a week later, she said.

The next night, the police said, Mr. Allen followed Ms. Gallagher home from a bar and offered her drugs outside her apartment on the Lower East Side. Surveillance footage showed her and Mr. Allen going into her building.

On the morning of July 24, less than a month before her 36th birthday, the police responded to a 911 call asking them to check on Ms. Gallagher. They found her lying in her bed, where she was pronounced dead. There were no obvious signs of trauma.

On Aug. 6, Chief Essig said Mr. Allen and Mr. Shirley followed Mr. Ahmed from a bar in Manhattan to the Bronx. He was found on a street at Heath Avenue and West 230th Street.

Memon Ahmed, his uncle, said that his nephew had gone to school to study information technology but ended up hating the field. He attended culinary school and was happy doing what he loved, Mr. Ahmed said.

“He was always a brilliant student,” he said. “We still don’t know what happened.”

The case against Mr. Allen and Mr. Shirley is separate from another against five other men who were accused in April in a series of druggings and killings. That group, prosecutors said, targeted the patrons of gay bars, raising fears in that community. A trial date has not been set in the case.