A man returned home from holiday to find a 4ft high electronic organ in his garden.
The instrument came complete with music sheets and needed the strength of a number of police officers to move it.
The householder returned to his home in the Lowfields area of Ingleby Barwick to find the organ outside his back window.
Sergeant Dave Hill, of Thornaby police, said: "The Dutch organ is quite large and very heavy. It is over 4ft tall and 4ft high and it is a complete mystery as to how it appeared in this man's garden.
"If anyone can identify the organ or has any information I would urge them to get in touch."
Anyone with any information is asked to contact sgt Hill on (01642) 302226.
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