Toan Truong, 43, was killed at his home in Allison Street, Sunshine West on February 3.

It is believed Mr Toan may have been killed by a gang who use infrared cameras to find houses that could be growing hydroponic marijuana in Melbourne's western suburbs.

The gang, which is fluid and could contain as many as 50 members, is believed to also be responsible for a string of armed robberies.

The cameras used by the gang - including one stolen from a fire station - can identify houses which are radiating more heat than normal, because of the operation of hydroponic equipment.

Gang members started flexing their muscle last year, when another man who had invaded several growing houses in the region was jailed and they filled the void.

Mr Toan had been growing marijuana in an upstairs bedroom, and had told his wife she was not to go upstairs as he was renovating in preparation for the baby and wanted it to be a surprise.

He was asleep at the house about 5am when his wife, who was eight months pregnant, heard a noise.

She went to investigate and found a man inside.

Mr Toan went to assist his wife and chased the man to a rear bedroom of the house.

The man fired two shots, fatally wounding Mr Toan in front of his wife and child.

The man fled in a vehicle parked nearby.

Detectives believe the offender was aware of the cannabis crop and had entered the house to steal the cannabis.

Homicide squad Detective Inspector Mick Hughes confirmed detectives were investigating links to a series of home invasions at crop houses, including a bungled attempt at Taylors Hill on Monday, which resulted in a man who had been carrying a gun being critically injured when he was hit by a car.

Detective Inspector Hughes said it appeared Mr Toan, who was working as a full-time engineer and was not known to police, had started growing marijuana for added income, but had yet to harvest a crop.

"Here you've got a...decent man from a good family, who actually had a really good job," he said.

"For some reason he decided perhaps he could make some money from growing a hydroponic crop and he's paid the extreme price for that mistake."

Tai Truong said his family had struggled to comprehend why his brother had taken such a shocking and inexplicable risk as they did not need money.

He said the family were not wealthy, but always knew "where the next meal was coming from".

Mr Tai said Mr Toan's wife had since given birth to a girl. She was struggling to "glue" the thousands of broken pieces of her life together and remained extremely traumatised.

"He was your stereotypical larrikin," he said.

"He was loved by his friends and his family. He had the world ahead of him."

Police have released an image of the man who was in the property, and obtained CCTV footage which shows a dark sedan speeding from the scene towards Fitzgerald Road shortly after the shooting.

Two cars were also seen travelling in convoy in the area about 45 minutes before the murder.

They are believed to be dark, one a late model Ford Falcon sedan and the second a BMW two door coupe or similar.

There were possibly three men in the cars.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000 or via crimestoppers.com.au.