A man accused of murder has had the case against him dropped after new evidence from post-mortem tests.
John O'Kelly, from Blandford, Dorset, maintained he hit Andrew Quelch once in self-defence. Mr Quelch, 48, was later found dead at his Dorchester flat.
Mr O'Kelly, 55, was due to appear at Winchester Crown Court to enter a plea on Friday but the Crown Prosecution Service (CPS) has now dropped the case.
The CPS said it could not prove he acted excessively or unreasonably.
Fiona Rutherford, from Dorset CPS, said: "All cases are kept under constant review, in this case new evidence from the post-mortem report became available following the decision to charge Mr O'Kelly.
'Sympathies with family'
"[The report] said that anyone struck in this way, after initial dazing, may well return to a normal state of consciousness followed by a lapse into deep unconsciousness, which is what the evidence suggests happened here.
"This report is consistent with Mr O'Kellly's account and his defence of self defence.
"The law does not expect anyone to exactly weigh up the force they use in self defence, and given the evidence proves that there was only one blow, we cannot prove Mr O'Kelly acted excessively or unreasonably in this case.
"This left us no other option but to formally stop proceedings against Mr O'Kelly.
"Our sympathies are with Mr Quelch's family at this time, who we have written to and have offered to meet face to face to explain our decision to them."