His name is Samuel Little, but for the experienced detective Tim Marcia, this 79-year-old man is "pure evil".
The American, sentenced to three life sentences for the murder of three women in Los Angeles, is currently in a Texas penitentiary, where he decided to talk about his criminal past.
He claims to have killed at least 90 people between 1970 and 2013. If the confession is true, Little would be the convicted serial killer who killed the most in modern American history.
The amount of detail about the murders Little said he committed, mostly against women, shocked police and prosecutors.
So far, investigators around the United States have identified evidence that links Samuel Little to nine of the murders he confessed.
Many unsolved cases, which were filed in at least 14 American states, are being cleared and re-examined in the light of his revelations.
The victims: poor or drug addicted women
Little has been in prison since 2013 in Los Angeles for the murder of three women between 1987 and 1989, crimes for which he is serving three life sentences.
But last July, DNA samples confirmed his connection to the death of Denise Christie Brothers, which led to his transfer to a prison in Ector County, Texas.
There, a detective identified by The Washington Post as James Holland gained Little's trust and managed to get him to talk about other crimes he had committed in the past.
The former boxer has accumulated, over five decades, a hundred arrests on charges of crimes such as kidnapping, rape and armed robbery.
But several times he managed to leave the prison, reports Beth Silverman, a Los Angeles prosecutor responsible for the process that led to the three convictions.
The confessions show that the victims were mostly poor women or those with addiction to alcohol or other drugs, investigators say.
Cases involving this type of victim often have a lower settlement rate in the United States, which may have contributed to Samuel Little's impunity over the years.
Strangulation as a brand
According to the American newspapers The Washington Post and The New York Times, the criminal gained the trust of the victims and then attacked, raped and strangled them to death.
Prosecutor Beth Silverman said the crimes were sexually motivated, but Samuel Little is offended when he is called a rapist. He claimed erection problems, but investigators found semen in the bodies and clothes of his victims.
The way he achieves sexual satisfaction is during strangulation, Silverman told the New York newspaper.
One of Little's recently confessed cases involves Melissa Thomas, 24, whose naked body was found in 1996 in a cemetery in Opelousas, Louisiana.
Little told police he met the victim on the street and asked her to use drugs in his car. They parked next to the cemetery and when intercourse started, he says he caressed her neck.
"Why are you touching my neck? Are you a serial killer?" She asked, according to Little reported to the police officer in charge of the case, Crystal LeBlanc. Angered by Melissa Thomas's question, he killed her.
For LeBlanc, it is amazing how Little remembers the names of streets, bars and the location of the cemetery of the small church of Opelousas.
Their methods also shock researchers. The criminal used so much force that he even broke a victim's vetebral spine by hitting it in the abdomen.
'God knew everything'
In modern American history, Gary Ridgway, the Green River killer, is under arrest for the deaths of 49 people in the 1980s and 1990s.
Randy Kraft said he killed at least 65 people, but was convicted of killing 16 victims.
"When the investigations are over, we estimate that Samuel Little will be confirmed as one of the serial killers with the most victims in the history of the United States," Bobby Bland, a prosecutor in the Ector district in Texas, told The New York Times.
According to investigators, Little speaks with excitement about his crimes, even laughing when he remembers details. "He's a charismatic psychopath," say police officers who had contact with him.
Florida Detective Michael Mongeluzzo asked Little how he had managed to avoid being captured by the police. "I can enter my world and do what I want," he replied, referring to the poor and drug-affected neighborhoods in which he chose victims.
He also shows no remorse. Police officer Crystal LeBlanc said: "God made me this way, so why should I ask for forgiveness?" And he added, according to the New York Times: "God knew everything I did".
Her hope and that of other investigators is that dozens of closed cases will find a solution, now that Little has decided to talk about his past.