A 13-year-old girl was stripped and molested in Bihar's Jehanabad district on Sunday. The attack was filmed.
The video of the attack was posted on social media and has since been widely shared.
No one can be seen in the video coming to the girl's rescue.
In the video, the girl is seen trying to fight off her attackers as they laugh at her and tear her clothes off.
ANI reported Patna Zonal IG Nayyar Hasnain Khan as saying four people have been arrested in connection with the case.
"Faces of two people have been matched with people in the video and other two were making the clip. Other 4-5 people have been named by them," he added.
News reports said police were conducting door-to-door searches in the area. The attack had taken place in Bihar's Ramdani village near Bharthua town.
The reports said police were able to zero in on the attackers from a motorcycle seen in the video.
The cellphone on which the attack was filmed has also been recovered by police.
The reports quoted police as saying most of the attackers looked like they were in their teens.
4 people arrested in connection with the case. Faces of two people have been matched with people in the video & other two were making the clip.Other 4-5 people have been named by them. Search operation is underway: Nayyar Hasnain Khan, Patna Zonal IG on Jehanabad molestation case pic.twitter.com/FA9fU6ySIE