Additional Sessions Judge of Sambalgarh tehsil R R Bhadoria also imposed a fine of Rs 10,000 each on the convicts.
They robbed a farmer, Ramdayal Dhakat, of Rs 90,000 on June 15, 2006 after threatening him with a firearm.
The incident took place when Dhakat, a resident of Gastoli village near here, was returning home on a tractor after selling his agriculture produce, Additional Public Prosecutor Ramesh Verma said today.
During investigation, police found that Surendra Singh, the tractor driver, and three of his friends had planned and committed the crime, he added.
The Judge, after going through the material on record and statement of witnesses, pronounced the four guilty.
Besides Singh, the other three convicts are Ramniwas Gurjar, Kallan Shukla and Rajiv Sikarwar.
