Wichita ? The BTK serial killer may have taken a necklace from one of his victims in 1977 and given it to a woman he was dating at the time, authorities said Wednesday as they appealed to the public for help in finding the jewelry.

BTK has sent several letters to police since resurfacing last March. Police said the killer said he took items from the crime scene after killing Nancy Fox on Dec. 8, 1977.

The killer — known by the self-coined nickname BTK, which stands for “Bind, Torture, Kill” — is linked to eight unsolved homicides that terrorized Wichita, the first in 1974.

Police are now looking for a necklace described as a gold chain with two pearls that were set vertically.

“It is not that unusual for serial killers to take mementos from the scene and perhaps the value to them is to help refresh their memory and relish the occasion,” said Howard Brodsky, a Wichita psychologist involved in the investigation of BTK’s crimes in the late 1970s and early 1980s.

He likened such a possible gift as “eccentric re-gifting.”

“This guy has that sense of morbid irony of what he is doing: ‘Wouldn’t she just die if she knew that was taken from the crime scene of a murder I just did,'” he said.

Authorities are asking anyone who may have seen the necklace or received a similar necklace as a gift in December 1977 or early 1978 to call the BTK tip line. Police have received more than 5,000 tips since BTK resurfaced.

In March, The Wichita Eagle received a letter with information on an unsolved 1986 killing. The letter contained a copy of the victim’s driver’s license and photos of her taken after she was slain.

It was the first communication from the killer known as BTK in more than two decades, and police said it linked the serial killer to an eighth slaying. The other seven people were slain in the 1970s, with BTK claiming responsibility for those deaths in letters to the newspaper and a television station.

Brodsky said the idea of BTK having a girlfriend surprised him.

“Him trusting another woman doesn’t go with my model of who he is, not necessarily that my model is correct,” he said.