An FBI spokesman says authorities so far have confirmed Little's role in nearly three dozen cases.
The agency released 16 images Tuesday, drawn from memory by Samuel Little, who told authorities they are just some of the more than 90 people he killed over three decades.
Officers are said to be desperately scouring old case files and photographs to try and identify the Jane Does, but matching them up is proving to be a hard task.
The FBI says Little chose to kill marginalised and vulnerable women who were often involved in prostitution and addicted to drugs, and who often went unidentified or their deaths were not investigated.
ASSOCIATED PRESS This undated photo provided by the Ector County Texas Sheriff's Office shows confessed serial killer Samuel Little.
So far investigators have managed to link Little to 36 of his claims, spanning the width of the U.S., from LA to Washington DC.
Little has confessed to killing 93 people over more than three decades, starting in 1970.
Little is serving a life sentence in Texas after pleading guilty in December in Odessa to the 1994 strangulation of Denise Christie Brothers, whose body was found about a month after she disappeared.
The FBI has added the sketches to an interactive web page that pinpoints the locations and describes the victims of the murders Little claims to have committed.
"Over the course of that interview in May, he went through city and state and gave Ranger Holland the number of people he killed in each place", said Federal Bureau of Investigation analyst Christie Palazzolo. "Jackson, Mississippi - one; Cincinnati, Ohio - one; Phoenix, Arizona - three; Las Vegas, Nevada - one".
Authorities were able to place Little passing through the area at the time of the killing, and in exchange for a deal which moved him to a different prison, Little agreed to talk to investigators where he confessed to the murders. Many more are pending confirmation and a number remain uncorroborated.
No formal charges on any of the additional killings have yet been brought.
The FBI urged anyone with information about the victims to call or email analysts at the bureau's Violent Criminal Apprehension Program at 800-634-4097. It has also been updated to reflect that Little is in custody in California.
Little has told authorities he has murdered more than 90 people across the United States, including potential cases in Tennessee and Kentucky.