An angler died from a heart attack shortly after a row with two youngsters who allegedly threw rocks at him.
Charlie Hilder, 66, was pronounced dead in the grounds on Lullingstone Castle in Kent on May 28.
Witnesses said a row had broken out shortly before he died.
Today Kent Police said a post-mortem found that Mr Hilder, from Romford in Essex, died from a heart attack - but detectives are investigating what happened before the tragedy.
In a statement police said: "It is understood that, at around 5pm, Mr Hilder was fishing from a boat in a private lake when he saw two boys at the bank near to the weir and asked them to leave.
"A brief dispute took place, during which items were allegedly thrown towards Mr Hilder.
"Several minutes later a further verbal argument took place between the boys and Mr Hilder in a car park, which is by the lake and near the castle gate."
He collapsed at around 5.50pm, after the boys had left, police said.
Police are now trying to trace the youngsters - said to be white and aged between 11 and 18.
Detective Chief Inspector Ivan Beasley said: "We are seeking to obtain any information that can help us establish the full circumstances leading up to Mr Hilder’s death.
"We have now established that a man and a woman, aged around 20, were sunbathing or picnicking in the field near to the car park at around 5pm and would urge them to contact us at their earliest opportunity.
"We would also like to obtain any video that may have been recorded by motorists or cyclists who travelled along Castle Road or Shoreham Road, between 12pm and 7pm on 28 May.
"In addition to this, we would ask anyone who attended the Lullingstone Castle area to review personal photographs they have taken as they may feature the boys in the background.
"A person flying the drone in the area has made contact with our investigators following an earlier appeal and we are grateful for their assistance."
Dad-of-five Mr Hilder is believed to have been a member of the Kingfisher Angling and Preservation society, which has voiced members' sorrow at his death.
And his daughter Stephanie wrote: "Last night our hearts broke to hear that our dad sadly passed away.
"Words can't explain how we are feeling at the moment. Sleep well Dad. Give everyone a hug from me."
In a statement on the group's website, the angling society said: "The Society has been shocked and greatly saddened to hear of the death of Mr Charles Hilder at Lullingstone on Thursday 28 May 2020.
"Although the exact circumstances surrounding Charlie’s death are unclear we believe that he died after a confrontation with poachers."
