A dad-of-two suffered fatal injuries in a pub fight before flying on holiday and dying suddenly the next day, detectives believe.
Simon Marx, 42, was caught up in a fracas between two groups of men at the Newton Arms in Normoss in the early hours of last Saturday.
He flew to Turkey hours later, and died suddenly the following day.
Detective Chief Inspector Gareth Willis, of Blackpool Police, said: “Mr Marx’s body has now been repatriated and a post-mortem carried out. As a result of its findings we have launched a murder investigation."
DCI Willis urged those who were drinking in the pub, in Staining Road, between 11pm on Friday, October 6, and 12.30am the following day, to come forward.
Detectives also want to speak to anybody who saw or spoke to Mr Marx, either face-to-face or on the phone, last Saturday before his flight.
"You may not think you saw anything significant, but we would urge you to contact us anyway as you may know or have seen more than you think," DCI Willis added.
The force did not comment on reports Mr Marx was hit with a glass bottle during the altercation, but said he died from a 'blunt head trauma'.
Four men from Blackpool were arrested on suspicion of murder. Three, aged 29, 29, and 52, were later bailed until Wednesday, November 1.
The fourth, 58, was released under investigation pending further enquiries.
In a statement last week, Mr Marx's family said there were 'all completely devastated by Simon’s sudden death.'
They added: “He was a much loved father, son, uncle and brother and he will be sorely missed by us all.
“We would ask that we are given some privacy at this time to try and start to come to terms with what has happened to our family.”
Kenny Stephenson from Blackpool Skip Hire, where Mr Marx worked as a driver, added: "The workplace today is of a very sombre mood and in a state of shock on hearing this tragic news.
"Simon was one of our own and as has been said always had the biggest smile and the ability to brighten anyone's day with his humour and happiness.
"He will be sadly missed by all his colleagues and friends."
Information can be reported to police by calling 101, quoting log number 40 of October 7.
Alternatively, Crimestoppers can be contacted anonymously on 0800 555 111 or online at crimestoppers-uk.org.