Central Bureau of Investigation (CBI) took over the Nithari killings case from the Noida police in January 2007.
It went on to present a watertight case against domestic help Surender Koli in the Aarti Prasad murder case that led to the designated court awarding Koli a death sentence on Wednesday.
The CBI, during its probe, had established the fact that Koli's employer businessman Moninder Singh Pandher was not present at his bungalow, D5, when Koli raped, killed then dismembered Prasad.
CBI's finding was based on Pandher's movements on the day the murder took place as established by the records on the location of his mobile phone gathered by its investigators.
The location of Pandher’s cell phone set, bearing number 9810098644, showed that at the time of the murder — between 11 am to 6 pm that day — he was in his Sector-2 office.
"He later went to east Delhi, then to Hotel Magpie of Haryana Tourism in Faridabad, where he spent the night on September 25, 2006, with a call girl," a CBI investigator said.
"The hotel's bills and the call girl's testimony proved Pandher's stay at the hotel."
The CBI had procured voluminous records from Pandher's cell phone service provider showing his location in 2005-06 that ran up to "3,000 pages".
According to the CBI, Koli killed his victims with a knife and not any sharp weapon "with teeth like saw" — a finding that was confirmed by a specially constituted medical board that examined the bone pieces.
"Pandher's phone records proved his absence from the crime scene so he wasn't charge sheeted," said CBI's prosecutor JP Sharma.
"It is clear that at the likely time of commission of offences against Aarti, which must be around noon on September 25, 2006, Pandher was at his office and he remained in Nithari for about one and a half hour later but did not return to his bungalow the whole night," according to the CBI charge-sheet.
It added, "This indicates the crime was committed by Surender Koli without the knowledge of Pandher."