A Brighton man suffered seven breaks to the bones in one arm and a double fracture to the jaw as he walked home from a party.
But no one can explain how he ended up with such serious injuries and Sussex Police are keen to hear from anyone who can help detectives solve the mysterious case.
The force said: “Mystery surrounds the circumstances around how a Brighton man came to suffer serious injuries when walking home from a Christmas party.
“Police were not initially called to the incident in Dyke Road Drive at around 2.15am on Sunday 13 December.
“The 31-year-old man’s wife was walking ahead of him at the bottom of the road when she heard a thud and ran back to find him bleeding from the mouth.
“An ambulance was called and he was taken to the Royal Sussex County Hospital where it emerged that he had suffered seven fractures to his left arm, two breaks in his jaw, numerous cuts and grazes and severe bruising to his head, right arm and the left side of his body.”
Detective Constable Sophie Tullett said: “This is a really unusual event in that it wasn’t initially reported to police until hospital staff advised him and his wife that his injuries were inconsistent with just a fall.
“We have made extensive house-to-house inquiries in the area and studied a lot of CCTV, but we have not been able to establish what or who led to the incident.
“It is possible that it may have been an assault or a hit and run but we can’t completely rule out a nasty and unfortunate accident.
“Shortly beforehand, his wife recalls seeing a tall man wearing a light or white top pass her walking towards Preston Road.
“We would like to speak to him as he may have important information that could assist our inquiry.
“Similarly, we would like to hear from anyone who was driving in the area at the time.”
Any witnesses or anyone with information is asked to phone Sussex Police on 101, email firstname.lastname@example.org or call the independent charity Crimestoppers anonymously on 0800 555111.