Barrie police have given residents permission to return to their homes for a second time, as investigators complete their explosives sweep of a house connected to a 30-year-old cold case.

"The evacuees of the area in and around 30 Virgilwood Crescent have been very kind, supportive and patient to all the officers involved, which was very much appreciated during this long complex situation," Barrie police said in a statement released early Saturday afternoon.

Twenty neighbouring homes were first evacuated Thursday when the search began. The approximately 60 residents were allowed back one week later after special teams of investigators declared the 30 Virgilwood Crescent property safe of improvised explosives and other hazards.

But on Friday, residents in four homes were asked to leave again after the discovery of an additional cache of hidden chemicals.

Residents in homes across the street were also told to stay out of their front yards while officers disposed of the new threat.

Butler said they found a total of 83 improvised explosive devices, a quantity of unidentified chemicals, 29 firearms and thousands of rounds of ammunition.

Police have said that 10 of the weapons were pulled from an underground fallout shelter that was dug into the home's backyard. The shelter's size was estimated at 4.5 metres long and more than two metres deep.

A father and his son had been living at the home, which Barrie officials told reporters may be demolished if city inspectors deem it unsafe.

Both men were charged last week in connection with the 34-year-old cold case involving the killing of Michael Traynor, a development that led police to check out the home.

Police say Donald Feldhoff, 54, is charged with first-degree murder in the 1978 slaying.

His 75-year-old father William has also been charged as an accessory after the fact.

With files from CBC News