When cops first discovered Pauline Henninghan, the body of the 67-year old grandmother was laying in the hallway of her apartment in a six-story public housing complex in Astoria, Queens.

Her clothes were stained with blood, detectives noted. There were cuts on her nose. Her scalp was tattooed with marks. And around her neck, resting loose like a wreath of costume jewelry, was the electrical cord used to strangle her.

The month was November, the year was 1989, and Henninghan’s homicide quickly turned cold. All case files were soon tucked into an anonymous folder marked Q89-6821 then stored in the basement of the 114th precinct.

“Leads had all dried up,” Lieutenant Richard Bellucci, commanding officer of the Queens Homicide Squad, told The New York Sun yesterday.

Now, after a two-year re-examination of the case and corroborating evidence from DNA testing, detectives believe they have solved the nearly 15-year-old crime. Yesterday prosecutors indicted Henninghan’s 51-year-old grandson, Kenneth Robinson, a Jamaica, Queens, man with a rap sheet for burglaries and drug possession, with her murder.

The tip that burst the case open again came from an unexpected source: an informant in Queens who had been arrested for jumping a subway turnstile without paying fare. The informant told police about Robinson’s involvement in the crime, detectives said, and they began to rifle through the dusty Henninghan case for clues.

The clue came in the form of a police photograph taken by Anthony Budney, the first detective to interview Mr. Robinson about his grandmother’s death. Mr. Budney, now retired, noticed that Mr. Robinson had a scratch on his neck and captured an image of the wound, but police never considered Robinson a suspect.

Jack Moser and Sergeant Jack Ryan, two detectives on the Queens squad, soon contacted Robinson, who was arrested this March for a felony burglary and drug possession charge. The detectives began to ask Robinson questions about Henninghan. He was uncooperative and defensive, detectives said, but agreed to a DNA test and forensic experts swabbed his mouth for saliva.

Matching Robinson’s DNA test results with DNA samples from 15-year-old matter taken from underneath the fingernail clippings of Henninghan, forensic experts came up with matching results and charged Robinson with his grandmother’s grisly murder.

The motive is unclear. Robinson could have been on a rampage for quick money, detectives now suspect, with Robinson itching to buy drugs in the middle of the night then raiding his grandmother’s home.

Robinson, through a court-appointed attorney, denied involvement in the crime.