Colin Hughes was attacked in Old Swan in September 2010 as he went to investigate a noise at the door of his  home.
Two men, aged 18 and 21, from Old Swan and Huyton, were arrested on suspicion of murder on Tuesday.
Detectives have arrested six people as part of the inquiry, but no-one has been charged.
Mr Hughes had been playing cards with his fiancee Paula Greenwood when they heard the glass in the back door smash at about 0045 BST on 21 September.
Ms Greenwood went to call the police while Mr Hughes, a chef at a local pub, went to investigate. She later found him lying face down in the garden.
He was taken to hospital but died soon afterwards. A post-mortem examination found he died from a single stab wound.

Sixteen men and eight women competed in the World Gravy Wrestling Championships at the Rose 'N' Bowl pub in Stacksteads, Lancashire.
Hundreds of people turned out to watch wrestlers from all over the country take part in the tenth event, held in aid of East Lancashire Hospice.
Organiser Andy Holt said it was "harder than it looks".
Mr Holt, who is the gravy monitor, has wrestled in the event eight times and said it was "very slippy out there".
He added: "It really does take it out of you, even if it is just two minutes."
The wrestling ring is a 14ft (4.3m) by 13ft (4m) pool which is padded to reduce the risk of injury.
Mr Holt, who makes the gravy at his black pudding factory, said he has had to change the recipe because the original attracted swarms of wasps to contestants.
Bouts are two minutes
Three judges award points on entertainment value, not just the wrestling
Losers get gravy bombed in the "laughing stocks"
Mr Holt said the best wrestler does not always win. He added: "The points system is more about entertainment."
Gandalf the Gravy (Joel Hicks), from Leicester, was defending the men's title, while Nicole Taylor-Lyons, 21, was aiming to recapture the women's event.
Mr Holt said: "It is crazy, but it is all about having fun and it is for a great cause."

Nine-month-old Millie Thompson, of Stockport, fatally choked on her lunch at Ramillies Hall School and Nursery in Cheadle Hulme in October 2012.
The review follows an e-petition set up by Millie's mother Joanne Thompson and a debate at Westminster Hall on Monday.
The government said it would consider making paediatric first aid mandatory.
Childcare and Education Minister Sam Gyimah said Millie's tragic death was "a wake-up call" and an independent review of early years educators was of "utmost importance".
He said: "We will produce guidance and, in due course, a national review which will include the question of mandatory training."
Mrs Thompson received more than 102,000 signatures in her online campaign to change the law and make it compulsory for all nursery staff to be trained in paediatric first aid.
Mr Gyimah praised Mrs Thompson and her husband Dan for setting up Millie's Trust, which provides paediatric first aid courses.
He said he would work with the couple to "ensure that there will not be another awful tragedy" like Millie's.
At the inquest into her death, South Manchester coroner John Pollard returned a verdict of misadventure and said no-one was to blame.
He said paediatric first aid training for all nursery staff was "matter of national importance".
The jury at Oldham Magistrates' Court heard that Millie started coughing and crying in a high chair while being fed shepherd's pie from a supervisor whose basic first aid certificate had expired.
The supervisor passed Millie to a colleague who had paediatric first aid training and gave the baby back slaps.
She was taken in an ambulance to hospital but was pronounced dead.

4 February 2014 Last updated at 06:29 GMT
Most students will learn European languages like French, German or Spanish - but Nel visited a school where students are learning the Chinese language Mandarin.
More than a billion people speak Mandarin in the world.
The Prime Minister believes learning the Chinese language will help Britain do more business with China.
Two men arrested over the killing of a 42-year-old man in his back garden in Liverpool have been released on bail.
[NEXT_CONCEPT]
Wrestlers in fancy dress have grappled for a world title in 1,000 litres of gravy.
[NEXT_CONCEPT]
A review of paediatric first aid training for nursery staff across England is to take place following the death of a baby in Greater Manchester.
[NEXT_CONCEPT]
From September primary schools across England will have to teach foreign languages.