A taxi driver who witnessed the aftermath of the incident in Edmonton, north London, told ITV News he saw police force their way into a house on Nightingale Road.
"They broke the door down and brought a man out," he said.
"There were dozens of police cars and a helicopter."
He added: "It's really worrying. It's very scary - we're always on the lookout."
More top news
Mostly cloudy overnight, but as low pressure systems feed in as the week goes on an unsettled period can be expected.
The hunt for murder suspect Jed Allen has ended after police found his body two days after discovering his mother, stepdad and sister dead.
Ben Stokes was in the thick of the action again as England completed a once highly improbable victory in the first Test aganist New Zealand