New York (CNN) -- Federal agents say a missing New Jersey woman may be one of 11 victims believed to have been slain by admitted serial killer Israel Keyes.
Investigators believe the woman Debra Feldman, 49, was last seen at her Hackensack home on April 8, 2009. She has not been heard from since.
The FBI said Keyes admitted that on April 9, 2009, he abducted a female from a state on the East Coast and transported her over multiple state lines into New York. Keyes said he killed the victim and buried her in upstate New York.
FBI Special Agent Barbara Woodruff told CNN Thursday that Keyes -- before he committed suicide last year -- was shown pictures of unsolved murder victims and people who had gone missing to see whether he would admit to being involved in any of those cases.
When Keyes was shown a picture of Feldman, he paused, looking at it a long time, before saying, "I'm not ready to talk about that one," according to Woodruff.
Footage on the FBI website shows Keyes during the interviews with federal agents, telling them he would release certain information or details about his victims, and then changing his mind.
"He did enjoy the cat and mouse game," Woodruff said.
Keyes committed suicide in his Alaska jail cell last December by slitting his wrist and strangling himself with bedding.
Investigators described Keyes as a kind of a murder addict who hunted victims in remote locations such as parks, campgrounds or hiking trails. An Army veteran and traveling contractor, Keyes studied other serial killers, but liked to say that he had not patterned himself after any other killer.
A multi-agency effort by the Anchorage police, the FBI and local law enforcement agencies in Lufkin, Texas, arrested Keyes in March 2012 for the abduction of Samantha Koenig, an 18-year-old barista. Her body was found in a lake in April 2012.
Keyes left many unanswered questions and a four-page note that expressed no remorse or clues to other slayings when he took his life.
Authorities are asking that anyone who may have information about Keyes or Feldman, or information about her around the time of her disappearance to contact the Hackensack Police Department or call 1-800-CALL-FBI.
CNN's Matt Smith, Mayra Cuevas and Brad Lendon contributed to this report