A large fire at a farm in Woodford near Thrapston is being treated as arson.
Police are investigating after the incident in Addington Road on Sunday (September 8) when hay bales were set alight.
Officers were called to reports of a large fire on the farmland next to the water tower at the Manor House Farm.
They are keen to identify a dog walker who may have witnessed three offenders running away from the fire, which is believed to have been started some time after 4pm.
A police spokesman said: "Police are keen to identify anyone else who may have seen how the fire started.
"Anyone who has any information about the incident should call Northamptonshire Police on 101."