Neighbours watch as police continue their investigation. (Jeff Semple/CBC)

Police in Barrie say 57 people are still barred from their homes as they continue their investigation of a local father and son.

Const. Angela Butler says an evacuation order is still in effect for 22 homes as police sift through a number of explosive devices and potentially dangerous chemicals found as part of the probe.

She says investigators will soon be detonating the six homemade explosive devices found at the scene.

Investigators from Toronto have been called in to help identify the chemicals and other substances found in the home.

The evacuation order went into effect after city and provincial police made an arrest in a 1978 murder case.

Donald Feldhoff, 54, has been charged with first-degree murder in the slaying of Michael Traynor, while his 75-year-old father William has been charged with being an accessory after the fact.