A pony harnessed to a trap died after it was forced into a Hampshire lake by a dozen people, the RSPCA has said.
A member of the public who tried to rescue the animal from Hawley Lake on Saturday afternoon was taken to hospital after the pony kicked out.
The animal was dragged down into the lake by its trap as it tried to swim.
Police also think an attempt was made to push a second pony into the water. Officers and the RSPCA are trying to establish a motive.
An RSPCA spokesperson said the group had lined up three ponies and encouraged them into the water.
One went in but when it tried to run free it was beaten back into the lake, he added.
Ministry of Defence divers and Hampshire fire service recovered the carcass.
The RSPCA said it was believed the group had brought the ponies to the lake.
The one that died was microchipped, but had recently been sold at market and the chip had not been updated.
The group was seen driving the surviving ponies along Minley Road in the direction of Yateley.
The injured man, a 21-year-old from Farnborough, was taken to Frimley Park Hospital in Surrey for treatment for a blow to the head and bruising.
Police appealed to people in the area at the time, including dog walkers and fishermen, to come forward.