The Bihar government has handed over the probe into the recent killings of social activists Mahesh Kant and Sarita to the Central Bureau of Investigation.

Speaking to reporters in Patna on Tuesday, ruling Rashtriya Janata Dal chief, Laloo Prasad Yadav, said after the people behind the brutal double-murder must be brought to book expeditiously.

Sarita and Mahesh Kant, activists of the Institute for Research and Action, were shot dead on Saturday night near Shabdo village in Gaya district when they were returning to their camp office in Fatehpur.

Gaya district police have arrested four persons in connection with the killings.

A strike called in two districts of Bihar -- Gaya and Jehanabad -- to protest the killings evoked a mixed response on Tuesday, officials said. The strike was called by the Communist Party of India-Marxist Leninist.

In Patna, CPI-ML activists took out a  morcha and shouted slogans demanding the arrest of the killers and dismissal of the Rabri Devi government.

Sarita and Mahesh Kant had changed the face of  Shabdo with community farming and use of innovative irrigational techniques.

A local criminal gang is suspected to be involved in the murders, a senior police official said.