Nearly 40 years after the daughter of a wealthy Toronto businessman was brutally murdered, police say they have narrowed her killer down to a member of one family tree and are close to knowing who did it.

Erin Gilmour, the daughter of mining magnate David Gilmour, was 22 years old when she was stabbed, strangled and sexually assaulted in her Yorkville apartment on the night of December 20, 1983.

She lived alone above the store she had been working at on Hazelton Avenue. Her boyfriend would make the grisly discovery at approximately 9:20 p.m.

Four months earlier, and fewer than three kilometres away, 45-year-old Susan Tice was found stabbed to death after being sexually assaulted in her Bickford Park home on Grace Street.

Hazleton Ave

Despite the close proximity of the two murders and the similar circumstances in which the victims were found, it would take another 17 years before the two crimes were linked by DNA evidence.

Now, 38 years after the killings took place, and thanks to the detective work in the decades that followed, police say they are closer than ever to catching the man responsible.

"We're on the right track," Det. Sgt. Stephen Smith told CTV News Toronto on Thursday. "We're very close to being able to narrow it down further where we can get to the point where we can identify the offender."

Susan Tice                             (Susan Tice is seen in this undated image. Source: Toronto Police Service)

Leaning on genetic genealogy and family tree websites, Smith, who heads the Toronto Police’s Cold Case and Missing Persons division, says he and his team have identified one family unit of interest, which encompasses all male relatives, including first cousins, brothers, fathers and sons.

"We're not talking 3,000, 5,000 people, but we're talking a family unit where there's a number of people still involved," Smith said, adding that he and his team are anxious to see more DNA testing processed before narrowing down their search even further.

'It's someone from a small town in Canada'

Remaining tight-lipped about specifics, Smith said the suspect is a man from a "small town in Canada" and that he was in Toronto at the time of the murders.

He revealed that the killer is part of a "very large" family unit.

A number of those family members were also living or visiting Toronto at the time of the murders.

"We do believe that at least a number of members of the family are still alive and living in small towns throughout Canada," Smith said.

Scene(A Toronto police detective investigates at the scene of Erin Gilmour's murder. Source: CTV News Toronto)

But it's unclear if the killer himself is alive today.

According to Smith, the chances of that are "50/50." Nevertheless, he says he hopes to make an arrest in the next "six to eight months."

Smith did not divulge any details about the family unit he’s investigating.

Questions also remain about whether the suspect knew his victims and what other murders he may have committed. However, Smith said that work can’t begin until after he is identified.

In the meantime, and as the total number of Toronto's cold cases near 700, Smith says the driving force behind identifying the killer in any cold case investigation is simple: closure.

"Most of the motivation comes from the family members. We speak to the family members in, I would say, at least 100, maybe more, of our murders on a weekly or bi-weekly basis," Smith said.

"The drive of the family members to get closure, to find out not necessarily why their loved one was killed, but who killed them, it gives us motivation to keep these at the top of our mind."

Smith said that he and his team want "nothing more" than to bring that peace of mind to all 700 families and to answer the questions that have lingered in their loved one’s absence.