Police in Sunbury, Pennsylvania, are now investigating 19-year-old Miranda Barbour's claims of killing at least 22 others from Alaska to North Carolina in what she said was part of her involvement in a satanic cult.
Police chief Steve Mazzeo said investigators had contacted the FBI and police in several other states.
Prosecutors are seeking the death penalty for Barbour and her husband Elytte, 22, for the murder of Troy LaFerrara, who they met through Craigslist, in November.
"I feel it is time to get all of this out. I don't care if people believe me. I just want to get it out," told a newspaper interviewer.
Elytte Barbour allegedly told investigators the couple wanted to kill together.
They told police Miranda Barbour stabbed Mr LaFerrara in the front seat of her car while her husband held a cord around his neck.