All they had to begin with was DNA samples found on the nine-year-old victim whose body was found inside a locked hutment in Vatsalatai Nagar slum in Nehru Nagar.
This was the third in four months but the police did not have any witnesses who could provide leads on the suspect. Challenged by these incidents, the police formed 27 teams to investigate the cases.
The police began keeping a watch on all those who held a previous criminal record or who were seen in the area before the murders.
They paid special attention to people who were known to have sexual perversions.
The police then decided to look at all those people who had access to the area and visited it frequently. It was then that the 19-year-old they finally arrested came into picture. He worked with a cable operator named Raju Patil and was often seen in the locality.
"He collected dues, provided cable connections and also helped solve problems regarding the cable network in the neighbourhood," Police Commissioner Sanjeev Dayal said.
The post-mortem report of the third victim had showed undigested food in her stomach, which indicated that she had died soon after having her meal. "Nail clippings of the girl were sent to the forensic sciences laboratory," Dayal said.
Body tissues of the attacker, lodged in the girl’s nails during a probable struggle between the two, were sent for DNA analysis.
The DNA of the accused was among more than 100 DNA samples that were sent to the forensic sciences laboratory for examination.
Once the laboratory confirmed that they had found a match in the DNA of the accused, did the police arrest him.
Dayal, however, did not comment on how often the accused visited the victim’s house or if they knew each other. "We have just obtained his custody and we need to interrogate him," he said.
The commissioner added that no two cases were similar and the same investigation procedure may not be applied to the other two unsolved cases.
(Names of the accused and his family have been withheld as charges are yet to be established)