Sarah Gatt's decomposing body was found in a bathtub at her home just north of the Melbourne CBD on January 3 last year.

Police now say the mother-of-four died as many as eight months earlier and that, in a bizarre twist, those who knew she was dead pretended she was alive and well.

Homicide Squad detectives today revealed officers entered Gatt's home on Lambeth St in Kensington about 2.30pm on January 3 for an unrelated matter.

When they entered, it was immediately clear that something was not right. The 40-year-old's body was located soon after officers detected an unusual smell. They found her body decomposing in the bathtub.

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Bags of evidence were removed from the home. Photo / News Corp Australia
Bags of evidence were removed from the home. Photo / News Corp Australia

Forensic teams sealed off the home and began investigating. More than two months after she was found, police say they suspect foul play.

"Investigators believe Sarah died between April 20 to 24. Forensic evidence has indicated that a violent assault took place within the premises," Victoria Police said in a statement today.

"They also believe that her body was deliberately concealed at the address and conscious steps were taken to imply she was still alive after her death."

Police arrested three men and two women shortly after the discovery of Gatt's body. They say all were questioned by police but none were charged. All five were released pending further inquiries.

Officer in charge of the Homicide Squad, Detective Inspector Tim Day, said police were keen to speak to anyone who believed Gatt was alive after April last year.

"It's disturbing and concerning to investigators that it appears someone has deliberately attempted to make it look as though Sarah was still alive," he said.

"There are people out there who know what happened to Sarah and we are urging them to come forward and speak to police.

"We are particularly keen to speak to anyone who saw any person coming or going from her Lambeth St unit after April 20 last year."

He said that could include "a range of people including neighbours, friends, passers-by or any local businesses she had contact with."

Gatt had four children, however none of them were living with her at the property at the time of her death.