Three teenagers and a 21-year-old man have been arrested on suspicion of murdering Pc Andrew Harper, who died while responding to reports of a burglary last month.
Thames Valley Police said the arrests were made by more than 100 officers in Berkshire and Hampshire on Tuesday.
Pc Harper was killed in the line of duty on August 15 in Sulhamstead, Berkshire.
The three teenagers had been previously arrested and released, while the 21-year-old was arrested for the first time in connection with Pc Harper's death.
The new arrests had been made following new evidence which had come to light, the police said.
In a statement, Thames Valley Police said: "The three people, who are all male, were originally arrested on Friday, 16 August. They were then released on bail until Thursday, 12 September, and were then re-bailed until 16 November.
"They are an 18-year-old man and two 17-year-old boys, all from the Reading area.
"Today, they have been re-arrested along with a 21-year-old man from Basingstoke, who has been arrested for the first time in connection with this investigation. They are all currently in police custody."
Detective Superintendent Ailsa Kent, of the Thames Valley Police Major Crime Unit, said: "We are continuing to investigate the death of our colleague PC Andrew Harper, and today we have re-arrested three people in connection with this.
"In addition to these re-arrests, we have also arrested a further suspect, a 21-year-old man from Basingstoke.
"All four have been arrested on suspicion of murder and theft and are in our custody.
"This follows new evidence coming to light as the investigation has progressed in recent weeks.
She added: "This is an ongoing, complex investigation, and we remain committed to achieving justice for PC Harper, his family, friends and colleagues.
"I would also like to reiterate our appeal for anyone who knows anything about this incident to come forward and talk to police, if you have not already done so.
"Anyone with any information, no matter how insignificant it may seem, should call the Thames Valley Police non-emergency number on 101."