Seth intercepted the girl when she was returning home after giving a lunch box to her father in a nearby crop field and and took her to a secluded place. He then strangulated her before violating her corpse.
He was later arrested and charge-sheeted on the basis of the information provided by eyewitnesses.
"The judge described the crime as rarest of the rare," government lawyer Parsuram Mohapatra said. Defence lawyer Anil Goyal said his client would move a higher court against the sentence.