Police said the accused Avadhesh, arrested on Monday night, is familiar with the victim's family and is a distant relative. He stayed in a neighbouring house near the victim -- seven-year-old Ashish -- in Swaroop Nagar in west Delhi.
"Avadhesh told police Ashish's parents used to abuse him in his absence and did not like his visits to their house," Deputy Commissioner of Police Aslam Khan told IANS.
"He killed Ashish after calling him to his room on the pretext of gifting him a cycle. He then asked Ashish what does his father (Karan Singh) think about him. When Ashish replied that Karan asked him not to visit his house, Avadhesh smothered him to death, wrapped the body and placed it in a cupboard. He, however, pretended to be a well-wisher before Ashish's family," she added.
"He did not try to dump the body as he knew CCTVs are installed in the streets. Instead, he killed some rats and placed them in his room. When asked about the stink, he showed one of the rats," she added.
He also bought some perfume, room fresheners and incense sticks to suppress the stink. He slept 37 days on the same bed under which he placed the cupboard with the body, police said.
"He was planning to dispose off the body at an isolated place so that he could later make a ransom call of Rs 15 lakh," the police officer said, adding: "We have recovered the body and sent it for post mortem."
Avadhesh also lied to Ashish's family and said he works with the Central Bureau of Investigation (CBI). He told police he was preparing for a competitive examination and also appeared for an UPSC examination thrice.
"During investigation, police teams examined all CCTV footage, took help of local surveillance but did not get any solid lead to track the minor boy," DCP Khan said.
"Since no ransom call was made, we investigated the case from all possible angles instead of kidnapping. During investigation, Avadhesh presented himself as a very confident person. Police teams recorded his, other family members' and others' statements," she said.
The victim's parents, who run a grocery shop, suspected Avadhesh after he stopped visiting their house since the last three days. He was a frequent visitor earlier.
"The family informed police and during cross checking, Avadhesh changed his statements continuously. At last, he broke down and confessed to his crime," the officer added.
Avadhesh also made false promises to Ashish's grandfather that he would get his son employed with the CBI.