Why would an investigating detective remain outside the scene for "continuity"

Factual Questions
1

I have been watching these two (1 & 2) full-length police interrogation videos from Toronto, Canada and the detective in charge of the case mentions that for “continuity” he remained outside the home of the accused during the search (for weapons and bomb-making materials).

What is the legal or investigative principal at play here that would result in the detective remaining outside of the site where the search-warrant was served?

You can read a transcript of the relevant part of the video by clicking here or goto 59:41 in the video.

2

My guess is that as the officer in charge of the investigation, he did not want to be involved in the chain of continuity of evidence, to avoid any blurring between his role as O/C and the evidence-gathering role of his subordinates. They probably want a clear demarcation of roles. The greater the number of people who get involved in the chain of continuity, the greater the chance of a cock-up.

3

I have no idea. And I have participated in many searches and obtained search warrants myself. If I wrote up the warrant I am certainly going to be leading the search. By no means will I be alone. It is not a one person job. Just as long as everyone’s role and actions are documented.

4

My only guess would be that on a large department they have a separate unit that handles such things. It would have to be a big city department. No legal reason I can think of just local policy.

5

If the detective had been at the site of the bombing, he might avoid entering the house being searched, to avoid the possibility that traces of bomb-making materials found in the house had been inadvertantly brought in on his person.

6

I’m thinking this is it.

Imagine;

Detective tracks all over scene of bombing, getting chemical traces all over himself.
Then goes to ‘suspects’ house and tracks chemical traces all over.
Bomb sniffer discovers traces in suspects house.
Attorney points this out in trial.
Evidence thrown out.

7

Except that if what they found was that their dog started getting excited inside the house they wouldn’t have a case to go to trial with. He could be excited about bacon (or in this case, back bacon). They were looking for bomb making materials and weapons. Unless you think he could track that in on his shoe.