Mr McMurdo's body was found outside his home on Friday but police are not saying when they think he died or how.
Police launched the homicide inquiry because "it is clear another person was involved in his death", Mr Cramer said.
Mr McMurdo, 32, had lived in Helensville for much of his life and was well known in the small semi-rural community.
He worked as a truck driver and was involved in transporting flowers.
He had three children, aged 12, 3 and a few months.
"Any small community reels at the prospect of someone having possibly been murdered in their midst," Mr Cramer said.
"There are a lot of people stunned by this. His family are obviously devastated."
Close family members, including his daughter, found his body.
Mr Cramer appealed to anyone who had been in contact with Mr McMurdo recently to contact police.
"Any information we can get, no matter how small it may seem, could help up us find out what happened."
- NZPA