"Every crime has a logic. To solve a crime, you have to study psychology and human behaviour," says 64-year-old Sobhraj, who is keenly following media reports about the mysterious murder of the teen in her own home in New Delhi's Noida suburb.
Aarushi was found dead May 16. The police initially named the Talwars' domestic help Hemraj as the prime suspect, but had to retract after his body was found the next day on the terrace of the house. Aarushi's father Rajesh Talwar was arrested May 23 and police said he killed his daughter in a fit of rage as he objected to her alleged closeness with Hemraj.
A second arrest in the case was made June 13 when the CBI held Talwar's compounder Krishna. Later, they arrested Rajkumar, the domestic help of Aarushi's father's business partner. Krishna and Rajkumar, both Nepalis, were subjected to narco tests.
Sobhraj, who had been behind bars in India in the 90s, says the CBI-conducted narco tests would not be accepted by any Indian court.
Under the influence of drugs, Rajkumar is recently reported to have told investigators that Krishna was humiliated by Aarushi's father and wanted to take revenge.
Accordingly, he, Krishna and Hemraj went to Aaurushi's room on that fateful night in May. Rajkumar reportedly told CBI investigators after the recent test in Bangalore, which is being hailed as a breakthrough in the murder case.
He also reportedly said he attempted to rape Aarushi and when she resisted, Krishna slit her throat with a khukuri - the sharp dagger used in Nepal - to silence her.
Rajkumar also reportedly said that when Hemraj got cold feet and said he would tell Aarushi's father everything, they killed him.
"CBI never took the permission of any court to administer the narco-tests," Sobhraj told IANS in Kathmandu's central jail.
"Therefore, it is illegal. Also, under Section 164 of the IPC, a confession is valid only when it is recorded before a magistrate, who has to be satisfied that it was not made under any coercion or inducement.
The drug Pentathol is used for these narco-tests. So the tests definitely fall under the category of inducement. Also, the effect of Pentathol is to make you very susceptible to suggestions. If your interrogator poses any question in a suggestive manner, under the influence of the drug you are likely to say what he wants you to say," Sobhraj said.
Sobhraj says the CBI, being under intense pressure from the media, resorted to the tests in order to find a scapegoat.
"The post mortem report and the girl's father's statement are at loggerheads," Sobhraj says. "The first says she was killed in the morning while her father says she was alive in the afternoon. It means till now, they have not been able to establish the actual time of death and are trying to juggle facts to fit the post mortem report."
According to Sobhraj, who himself knows how it is to be pursued by the media, no human right organisations took up cudgels on behalf of Krishna and Rajkumar because "they are not Indians".
However, the issue has generated heat in Nepal, with a leading daily writing that Nepalis were being victimised in India.
Sobhraj feels the murder was committed by someone for whom it was his first crime. That is why police are finding it difficult to catch him since the perpetrator would not have any previous record.
"I feel it could be a case of jealousy," he says. "It could be the result of rivalry between two boyfriends. But whoever it was must have been known to the girl and trusted by her."
The police's best hope would be, he says, if someone close to the "boyfriend murderer", who suspects something amiss, comes forward with information.