Five of the dead birds were autopsied by the National Veterinary Institute, (Statens veterinärmedicinska anstalt, SVA) and results showed that the birds had died of acute blunt force.
According to Marianne Elvander, zoologist at SVA, the jackdaws were killed by severe internal bleeding. None of the birds showed sign of infection or illness.
"Our assessment is that they weren't carrying any contagious disease, but figuring out exactly what did kill them, other than being some sort of external force, is rather outside our area," said Olov Andersson, SVA's information officer, to TT news agency.
"What comes to mind is that they may have flown up, and been hit, or something of the sort," he speculated, a theory defended by most experts.
The birds may have been frightened by something in the middle of the night, flown about blindly, and died in collisions with different objects in the dark.
"Jackdaws overnight in trees in huge flocks. If something scares them, hundreds of birds can take to the skies as one," Anders Wirdheim of the Swedish Ornithological Society (Sveriges ornitologiska förening, SOF) told TT.
The jackdaws were discovered on a street in Falköping, just before midnight on the night between Tuesday and Wednesday. In total, between 50 and 100 dead birds were found.
Similar events have recently been reported from at least two US locations. A few days ago, 5000 birds were found dead in a town in Arkansas, and some days later a similar mass death occurred in Louisiana, as 500 birds plummeted from the sky.