They said accused Ramkumar Sahani (27) was in love with the victim's aunt. However, since the family members of the child did not approve of the one-sided affair, he decided to kidnap the boy.
The accused worked in a local factory and lived in the neighbourhood, they said.
On August 30, Ramkumar abducted the child and took him to Delhi, Jalandhar and Bihar and finally landed in Haridwar. He then called up the boy's father to deposit Rs 5,000 in the account of a certain person.
The Thane police, which had launched a search for the abductor, finally traced him to Haridwar based on the phone call records and arrested him from his friend's house there.
The accused was then brought back to Thane by police, who obtained a transit remand from Haridwar court after the arrest by Uttaranchal police.
"The kidnapped boy as well as the accused were brought back to Thane today and the child was reunited with his parents who were anxiously waiting for him," police said.
The accused has been booked under various sections of the IPC, police said.