. . . I know manual it was a loud buzzer/bell I think?
That doesn't make sense, as "linking up" has no obvious connection with a buzzer/bell or its loudness. The BT operator explained that she didn't use a '999' line for the link-up anyway.
I was just stating when it was Manually operated a loud Buzzer would sound and the operator would connect, obviously Maldon exchange transferred from manual to auto in 1966 and electronic after the murders, Roch is asking to link open lines at the time of murderer (auto) and I don't know how they did it?
1937
The 999 emergency telephone service was made available to London subscribers from 30 June and was later extended throughout the country. When 999 was dialled a buzzer sounded in the exchange and a red light flashed to draw an operator's immediate attention.
This was very far removed from the sophisticated information service designed by BT and launched on 6 October 1998. The new information service allowed details of both the calling number and the address from which a 999 call had been made to be transferred automatically to the emergency authority operator’s screen.