The police on Friday arrested the biological and foster parents of the minor girl, who was shot dead along with Haryana Police sub-inspector Narender Kumar outside the mini-secretariat in Rohtak on Wednesday, in connection with the murders.
A team led by Arya Nagar police station SHO inspector Sunita made the arrests. The foster father had adopted the girl from his brother-in-law in 2002.
During interrogation, the two couples purportedly told the police that they were unhappy with the girl for eloping with and marrying a Dalit youth. The four allegedly hatched a conspiracy with her cousin, who called his friends from UP for committing the murder.
The accused allegedly conducted a reconnaissance of the court premises on July 25.
The police said raids are being conducted to arrest the remaining accused.
Relevant sections under the Scheduled Castes and Scheduled Tribes (Prevention of Atrocities) Act have also been invoked, they added.