Neighbours have described an altercation in a residential street shortly before a man was shot dead by police.
The man in his 40s, believed to be the father of three teenagers, was fatally shot at 8pm on Wednesday.
Cambridgeshire Police had been called to Duck Lane, St Neots, over concerns for people involved in the trouble, 15 minutes earlier.
Residents reported hearing raised voices shortly before the police arrived.
One said: "We had never seen any trouble at that house before - it's not like somewhere the police are out all the time.
"But there was definitely some kind of row last night. We heard shouting for a few minutes then it seemed to die down."
A forensic tent has been erected outside the terraced property and parts of the street have been cordoned off by police.
A Cambridgeshire Police spokesman added: "The man died at the scene. No one else was injured in the incident."
Neighbours described hearing two or three loud bangs, which they initially thought were fireworks or television sound effects. One woman, who knew the family who lived at the terraced house, said that a man and woman with three teenage children lived there.
She added: "Our kids used to play with theirs, they were a nice family. There was never any trouble at that house, unlike some around here.
"They just seemed like a nice, normal family so I can't think what happened. It's terrible."
Mary Bath, 65, said her husband rushed outside after hearing the commotion but police told him to go back inside for his own safety.
She added: "I knew the couple from seeing them around and they seemed nice. "We heard the bangs and joked it sounded like gunfire. Suddenly there were police everywhere and we realised it was serious.
"It's an awful thing to happen and we're all very upset."
The Independent Police Complaints Commission (IPCC) is investigating the incident.
A spokesman said the commission was contacted by Cambridgeshire Police on Wednesday night and declared an independent investigation at about at about 9.30pm.
He added: "The man's next of kin have been informed of his death and the area will remain cordoned off for some time whilst IPCC investigators undertake the scene management process. The investigation is in the very early stages and we are unable to provide further details at this time."