Two “closely related” men were shot dead in two villages six miles apart in what police described as targeted attacks.
Three people have been arrested on suspicion of conspiracy to murder, Cambridgeshire Police said, adding officers do not believe there is a risk to the public.
Officers arrived to find the body of a 32-year-old man with a gunshot wound inside a property and are treating his death as murder.
The body of a 57-year-old man with gunshot wounds was found at a property in The Row and his death is also being treated as murder.
He added: “We do not believe there is any ongoing risk to the public in Cambridgeshire. We have got full control.”
Neighbours near two semi-detached houses sealed off by murder detectives in Sutton described hearing gunshots and seeing armed police arrive shortly after.
Gordon Murray, who watched events unfold from his window, saw police cars “racing down” and armed police shouting on Wednesday evening.
“I saw the police cars racing down here,” he said.
“There was a lot of shouting.
“I thought it was an altercation or something. Then I saw the armed police.
“They were shouting something to the homeowners. That was it.”
He added: “My son said he heard some bangs but I don’t know if that was the car doors slamming.
“There was a white hatchback which came around and stopped outside, then about half an hour later he came back and lifted up the boot.”
Mr Murray said the footage was “a bit fuzzy, it was dark”.
Sarah Lown, who also lives nearby, said she heard three loud bangs on Wednesday evening.
“I didn’t know it was gunshots at the time,” the 38-year-old designer said.
“It was about 9.15pm; I thought it was something blowing over as I heard a bang.
“There are pallets in our garden that I thought could have fallen over.
“I didn’t think anything crazy had happened.
“I heard two more – it was bang, space, bang.
“Whether or not they were each gunshots I don’t know; then police were outside the house.”
Ms Lown said there were no sirens, “just the flashing lights”.
She said a man who lived at one of the properties sealed off by police “always had really fancy cars out the front, souped up, cool looking cars”.
“I don’t know if he worked with cars,” she said. “I had never met him so I don’t know.”
Police said they are not in a position to name either victim because formal identification has not been carried out.
A 27-year-old man and a 33-year-old woman were arrested in the early hours of Thursday in Cambridge, while a 66-year-old man was arrested in the Worcester area.
A white Peugeot 208 and shotgun have been recovered.
Detective Inspector Mark Butler, from the major crime unit, said: “These events will be shocking to local people and there will be understandable concerns within local communities, however, we are treating the attacks as targeted and there is no wider risk to the general public.”
Anyone with information is asked to call police on 101, quoting Operation Scan.