The accused, Rocky Yadav, was on Tuesday arrested from a house in Bodh Gaya, police said. He has confessed to his involvement in the murder, Gaya's Senior Superintendent of Police (SSP) Garima Malik told reporters.
Rocky allegedly shot dead Aditya, the teenaged son of a businessman, on Saturday night for overtaking his car on the Bodh Gaya-Gaya road.
Aditya's mother Chanda Sachdeva and his father Keshav Chand Sachdeva have demanded a speedy trial in the case to ensure that justice is done.
Additional Director General (police headquarters) Sunil Kumar said: "Police have been working with a time frame to complete investigations in the case within three weeks. The chargesheet will be filed within a month to ensure speedy trial of the accused."
The police have recovered the pistol used in the crime, SSP Malik said. "The licence for the pistol was issued in Delhi," she added.
Rocky will now be produced in the court, the SSP said.
Malik said some liquor bottles were recovered from the house of Rocky's mother Manorama Devi, who is a JD-U legislator.
"A separate case will be filed in this connection for violation of the liquor ban in Bihar," Malik told reporters.
Rocky's father Bindi Yadav is a criminal-turned-politician, who was with him along with a bodyguard when the crime took place.
Bindi and the bodyguard were arrested and sent to judicial custody by a local court.