Four others were sentenced to seven years in jail.
Vinubhai Vaghela, Bakaji Thakor, Ashokji Thakor and Jentibhai Thakor were sentenced to seven-year imprisonment for conspiring with Prajapati and Rabari, said advocate B A Tunwar, counsel for the victim's father.
Shah was kidnapped from near Ramji Mandir in Thara town of Kankrej taluka in Banaskantha on March 25, 2014.
The kidnappers had demanded a ransom of Rs 50 lakh from the boy's father, Trilokchand Shah, a trader and son of former MLA late Shantilal Shah.
The boy's body was fished out from the Narmada Canal four days later on March 29.
The convicts decided to kidnap the boy as Prajapati, who used to till Shah's land with his tractor, needed money for gambling, said Tunvar.
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