It is unheard of for "COMMANDER SHIP" of a police firearms operation to change hands in the middle of the same operation, so why was leadership changed just after three further bodies had been reportedly found upstairs (8.10am), where two bodies (7.37 - 7.41am) had previously been reportedly discovered upon entry to the premises?
Something went dramatically wrong soon after 8.10am, which led to a separate type of operation being mounted inside the premises, which PS Adams could not command from his position outside the premises, and explains why PI MONTGOMERY took Command from 8.15am, because he was inside the premises once the operation went pear-shaped...
The original scenario of two bodies downstairs / three bodies upstairs (by (8.10 am), altered into a different scenario of "0ne body downstairs / four bodies upstairs", from that point onwards, which is why MONTGOMERY became the Commander, from 8.15an, onwards...