Additional District Judge Krishna Pratap Singh found the four guilty in the kidnapping and murder case of a 16-year-old boy in 2011 and sentenced them to life imprisonment.
Mastermind of the crime, Ravi Kumar, who was known to the victim, is among the four awarded life sentence.
The court also slapped a fine of Rs 10,000 each on the four.
Two others accused are minor and their case is pending in juvenile court.
The kidnappers had demanded Rs 75 lakh ransom. The boy's body was found from a well in Sikrichak area of Patna the next day.