In Lucknow's Sugamau slum, a woman with a mental illness was badly beaten by a crowd of more than 40 people who wrongly thought she was trying to kidnap a child.
The attack left her injured and bleeding, and a video of the incident quickly spread online.
Police detain 2 after viral video
At first, local police downplayed what happened, calling it "minor," which delayed action.
But once senior officers saw the viral footage, they took two people into custody and are looking for others seen in the video.
Police say the woman was allegedly suspected of having come there to abduct a child, and they are investigating to make sure everyone responsible is held accountable.
The case has sparked fresh worries about mob violence in the area.