The color of their lipstick. The jewelry they wore. The city where he killed them.

Samuel Little confessed to more than 90 murders over three decades, making him one of the most prolific and sinister serial killers in U.S. history.

But many of those Little claims to have killed from 1970 to 2005 haven't been identified or linked to the killer, making it hard for law enforcement to verify his claims or know whether they are cold cases or people whose bodies have never been found.

The FBI is hoping to change that and on Tuesday released 16 ominous and eerily detailed portraits that Little drew of people, suspected of being his victims, from prison in Texas.

"We are hoping that someone - family member, former neighbor, friend - might recognize the victim and provide that crucial clue in helping authorities make an identification," FBI spokeswoman Shayne Buchwald said in a statement to USA TODAY. "We want to give these women their names back and their family some long-awaited answers. It’s the least we can do."

The drawings capture the color of each victim's eyes and how they wore their hair. One person, who Little says went by "Mary Ann" and he killed in Miami, is wearing a blue and grey headband, another who he claims to have murdered in Atlanta is wearing bright red lipstick and red earrings. Some appear to be grinning while others appear stern and stoic.

Each drawing is marked with a possible city and year in which the murder happened. Buchwald pointed out that Little's drawings are vividly accurate and have helped provide breaks in three cold cases across the U.S.

Indeed, the drawings and the massive confessions from Little in May, when he admitted to killing more than 90 people in exchange for a prison transfer, has energized local authorities across the nation who are now reexamining their unsolved cold cases.

Authorities in Maryland were able to use Little's description to link him to the murder of a woman who has never been identified. Another drawing helped authorities link Little to the 1984 murder of a woman in Arkansas, who also has not been identified.

More:FBI: A convicted killer admitted to 90 murders in exchange for a prison transfer

More:He may have found the body of a serial killer's victim. Now he needs to find her name.

In Mississippi, local investigators met with Little in prison. One lieutenant with the Pascagoula Police Department said Little has a "photographic memory" when it comes to the graphic details of his killings and offered the department specifics in how he met, loured and killed one woman in Pascagoula, a city along the Gulf of Mexico about 35 miles east of Gulfport.

The details helped link Little to remains that were discovered by hunters in the 1970s.

The killings went on for decades and mostly went unnoticed because Little did not focus his carnage on one particular area or city. The now 78-year-old took his vile killing spree across at least 16 states, strangling each of his victims.

Before the rise in technology, local authorities did not have access to databases and other means in communicating the specifics on certain crimes, making it hard to link crimes that may have happened hundreds of miles away or months or years later.

Little, 78, was arrested in 2012 in a shelter in Kentucky, then extradited to California on a narcotics charge. Los Angeles police obtained a DNA match to Little on three unsolved murders in the area in 1987 and 1989 and was charged with three counts of murder. In 2014, he was sentenced to three consecutive life sentences without parole.

As Little was awaiting trial in Los Angeles, authorities in at least nine other states began scouring cold case files to see if Little may be connected. Then in May, Little opened up about his other misdeeds in exchange for a prison transfer. He went through each city and state and told authorities the number of people he killed in each location.

Since that time, authorities have continued meeting with Little and have been able to corroborate more than 30 of the killings.

Anyone with information about the victims or the case can call the FBI's Violent Criminal Apprehension Program at (800) 634-4097.

Contributing: Alissa Zhu, Mississippi Clarion Ledger