Police Commando Shakti Singh was on duty and present in the police van when the incident took place on September 3, IG, Ajmer, Malini Srivastava said.
Three members of Anandpal's gang - Nirmal, Keshar and Mahendra Singh - were also arrested along with Shakti Singh.
The gang members planned the escape and Shakti Singh helped in executing the planning, she said.
Taking advantage of the situation, Anandpal and the other criminals escaped. The commando played important role in setting the criminals free, the IG said.
12 policemen, including the SHO of Parbatsar police station and commando Shakti Singh, have already been suspended for the incident.