The accused identified as Sonu (24), Shane Ali Khan (54) and his son Zeeshan Khan (20) were arrested following a tip-off, a senior police officer said.
They are accused of killing Kayamuddin Ansari, SHO of Kothi in Bihar's Gaya, on October 3 after he had objected to their extortion attempts in the area, he added.
His bullet-riddled body was found in fields after he had gone for a morning walk.
Preliminary investigation suggested that three men on a motorcycle shot the Station House Officer to death.
The accused will be produced in court and their transit remand will be sought, the official said.
Investigation is underway, he added.
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