The Special Task Force of Uttar Pradesh Police, which is probing the killings, detained 12 people and arrested a suspect named Tej Pal Singh.
Uttar Pradesh Police have now launched a hunt for others involved in the murders.
“We are on a lookout for the culprits, four teams have been dispatched to Madhya Pradesh and we hope to get a breakthrough soon,” Deputy Inspector General of police (DIG) V.K. Garg told IANS.
A Bharatiya Janata Party leader from Tikamgarh, Brajesh Tiwari and his wife Babli Tiwari (35), nephew Mayank (15) and son Puneet (12) were pumped with bullets on the highway near the Jhansi Medical College.
They were travelling in their car on way to attend a family wedding when another speeding car intercepted their vehicle and before they could understand what was happening, attackers fired 50 rounds, killing all people in the car.
Family members of Tiwari told police that they suspected a Samajwadi Party (SP) leader could be behind the killings.
Neeraj Tiwari, a close relative, said in past too after losing the elections, SP leader O.P. Arjariya and his supporters had fired at the family.
The killings of four people on the highway have sent shock waves in the region.