DNA evidence collected from a San Francisco basement where the “Night Stalker” raped and killed a 9-year-old girl in 1984 has produced a possible match to a second person, authorities said, but investigators have not linked the other individual to the crime and do not know whether he was in the basement at the same time.

Police officials confirmed Tuesday that they were looking into the second person, who was a juvenile at the time of Richard Ramirez’s slaying of Mei “Linda” Leung on April 10, 1984. Her body was found hanging over a pipe in the basement of her Tenderloin apartment building at 765 O’Farrell St.

The girl had been with her 8-year-old brother when she lost a dollar bill and went looking for it, police said. The boy wandered away, then came back to the basement and found his sister dead. The case remained unsolved for years — even after Ramirez’s capture in 1985.

Brutal attack

It was 2009 when police concluded the girl was beaten, raped and stabbed by Ramirez, a devil-worshiping serial killer who came to be known as the Night Stalker for a string of Southern California attacks in which he broke into homes and murdered people. He was ultimately convicted of 13 killings, but is suspected of several other slayings and attacks.

The pace and brutality of his spree — some victims were mutilated, their eyes gouged out — terrorized the state before he was spotted, subdued and pummeled by bystanders in 1985. He was sentenced to death in 1989, but died in 2013 from cancer.

In 2009, DNA evidence linked Ramirez to Mei’s rape and murder. At the time, The Chronicle reported that the evidence also revealed the possibility of a second suspect.

John Sanchez, crime lab manager for the San Francisco Police Department, said Tuesday that genetic material from a second individual — a much smaller sample than that of Ramirez — was uploaded to the FBI’s database in 2009 and returned a potential hit in 2012.

However, the genetic material from the second person did not represent a complete DNA profile and never should have been uploaded to the criminal database, Sanchez said, because incomplete profiles can result in false positives.

“It shouldn’t have gone in because it didn’t meet the standards,” he said. “Any ID (made from the flawed sample) would require further investigation.”

The New York Post reported Monday that the second DNA profile had been linked to a man who was a juvenile in 1984. Authorities have declined to name the person, who has not been charged with any crimes related to the killing.

San Francisco Police Chief Greg Suhr told KPIX-TV that investigators were familiar with the second person.

“There’s a handkerchief that was found, and there was a second sample on it,” Suhr said. “And we and the crime lab are trying to work to see if we can somehow connect this other person in some way to the offense.”

A spokesman for the San Francisco district attorney’s office said there was not enough evidence for additional charges.

“Richard Ramirez has been previously identified as a suspect in the gruesome murder of Mei Leung,” said Max Szabo in a written statement. “At this time there is insufficient evidence to charge anyone else in connection with this crime.”

L.A. slaying

Mei was slain more than two months before what had been Ramirez’s first known murder, the killing on June 28, 1984, of 79-year-old Jennie Vincow in the Glassell Park area of Los Angeles.

But Mei was not Ramirez’s only San Francisco victim. On Aug. 17, 1985, about two weeks before his arrest, Ramirez allegedly shot and killed a 66-year-old accountant, Peter Pan, as he slept in his home near Lake Merced. Pan’s wife, Barbara, who was beaten and shot, survived but was left disabled.

On the walls, the killer scrawled pentagrams and “Jack the Knife” in lipstick. Authorities later learned that someone matching Ramirez’s description had sold Barbara Pan’s jewelry in El Sobrante.

San Francisco police also have long suspected Ramirez of killing Masataka Kobayashi, 45, chef and part owner of Masa’s restaurant on Bush Street, on Nov. 13, 1984.

Kale Williams is a San Francisco Chronicle staff writer. Email: kwilliams@sfchronicle.com Twitter: @sfkale