A woman who suffered serious facial injuries from a corrosive substance could have "accidentally injured herself", police said.
Officers were initially called to reports of a substance being thrown in the area of Northbrook Street, Ladywood, Birmingham on Tuesday.
The woman, 47, remains in hospital in a serious condition.
Detectives said on Thursday they were "keeping an open mind" as to how she was injured.
In an update posted on social media, Birmingham police said officers were exploring a number of inquiries including the possibility the woman had accidentally injured herself.
The woman is receiving specialist burns treatment, ambulance staff said.
Police said it is thought a member of the public transported the victim to Astbury Avenue in Smethwick where an ambulance crew attended to her.
The victim's daughter previously told the BBC that her mother was in a critical condition in hospital, and she feared she may lose her eyesight.