The on-site portion of the investigation into a deadly house explosion in Mississauga last week has wrapped up but it could be some time before we know exactly what caused the blast.

Police confirmed last week that two people, 55-year-old Dianne Page and her husband 55-year-old Robert Nadler, were killed after a massive explosion levelled a home on Hickory Drive on the afternoon June 28.

The explosion led to the evacuation of several addresses and multiple homes sustained significant damage after heavy debris went flying hundreds of metres from the blast zone.

Speaking to reporters during an update Monday, Peel Regional Police Sgt. Josh Colley said that the Office of the Fire Marshal has concluded its on-scene investigation.

He added that some of the evidence collected as part of the case will need to be sent out for expert analysis.

“(It) could take some weeks with some of the evidence so it is hard to say exactly a time frame of when they will know the cause,” Colley said.

Colley said among the evidence that will be investigated is hand-written notes found at the scene that appear to be written by someone in distress.

“I think I spoke earlier about hand-writing analysis. The biggest portion is making sure that the letters are associated to the right addresses. There have been numerous houses that were destroyed. We just have to make sure what we have recovered thus far, we can put back the specific addresses.

He added that they still do not know if the cause is accidental or deliberate.

The autopsies on both victims have been completed but Colley said police will not be discussing those results.

Initially, 700 addresses in the surrounding area were under an evacuation order following the blast and during Monday’s update, Mississauga Fire Chief Tim Beckett said residents of 69 addresses are still not allowed to return to their homes.

“Over the past two days, we started yesterday afternoon and all through this afternoon, we will be working with the residents to get them back, at least, to their homes. Some of them will be able to enter their home on a 15-minute supervised visit to grab personal needs. The homes will then be turned over to their insurance companies so that they can be boarded up and secured,” Beckett said.

“Engineers need to be brought into the neighbourhood to really start assessing the true damage of the homes and at which point in time, work with the building officials will happen until we remedy the homes safe for occupancy.”

He added that it has been an “emotional time” for those impacted by the explosion.

“This is the first time is six days that some of these people have been allowed back in,” he said Monday.

“The damage that we have encountered as part of this explosion has been extensive.”

He added that some of the homes adjacent to the house where the explosion occurred will have to be torn down.