A woman was raped in a layby after stopping her car to investigate an empty child seat by the road.
The woman was driving along the A4 in Thatcham, in Berkshire, when she saw the seat near the junction with Cox's Lane.
She stopped her car around midnight out of concern that something may have happened to a child and was then attacked.
Thames Valley Police says it is increasing patrols in the area.
The victim did not know the offender and police are attempting to work out whether the seat was placed as a lure.
The force is asking for anyone with dash cam footage of the area, particularly between 11pm on Sunday and 12.15am on Monday, to come forward.
Alice Broad, detective inspector at Thames Valley Police, said: "The victim was driving on the A4 before the offence occurred.
"She stopped her vehicle at the scene because she saw a child’s car seat in a layby and was concerned there might be a child at risk because the car seat was empty.
"Thames Valley Police is working to understand the significance of the child's car seat and whether it is linked to the offence."
The force added that, to ensure the safety of the public, to make a note of the precise location and call Thames Valley Police on 101 if people see "anything in a road or on the roadside that concerns you".
"The force can then make appropriate checks," the police added.
"This is a concerning incident and one that has understandably caused anxiety in the local community.
"However, such offences are extremely rare and a thorough investigation is underway to identify the offender."
Anyone with any relevant information is asked to contact Thames Valley Police online or by calling 101 quoting incident 43210366130. Alternatively, people can contact Crimestoppers anonymously on 0800 555 111.