Another man has been arrested in London by detectives investigating the murder of 16-year-old Mary-Ann Leneghan.
Mary-Ann's body was found in a park in Reading
Police have also been given permission by a magistrate to question another man being held for a further 24 hours.
Adrian Thomas, 19, Indrit Krasniqi, 18 and Jamaile Morally, 21, have already been charged with the Reading murder.
The men, all from London, are also charged with kidnap and the attempted murder of Mary-Ann's 18-year-old friend, who survived being shot.
Mr Morally, 21, of Balham, south London, also faces a charge of raping Mary-Ann's friend, who cannot be named for legal reasons.
The 16-year-old's body was found in Prospect Park on 7 May. Her 18-year-old friend was alive.
A Thames Valley Police spokeswoman said the latest arrest was made at around 1900 BST on Sunday.
The man is being held at a police station in London.
Detectives are still appealing for more information.
Mr Thomas and Mr Krasniqi will appear before Reading magistrates on Monday, police said.
Two women and a man, also arrested in connection with the killing, were released on police bail on Saturday.
On Saturday Mr Morally was taken to hospital after an "incident" in a cell at the magistrates' court in Reading.
A Thames Valley Police spokeswoman said: "The man was not seriously injured. He is now on his way to Bullingdon Prison having left hospital."
Left for dead
Mr Morally was remanded in custody until 19 May when he will appear before Reading Crown Court.
Detective Superintendent Mark Warwick, who is heading the inquiry, said they still urged people to come forward and help police.
"There are people in the community that have information that could be valuable to us," he said.
According to police the girls were chatting in the car park of the Wallingford Arms, a disused pub near their homes, on Friday 6 May when they were forced into a car.
They were taken to the Abbey House Hotel, in Connaught Road, where it is alleged they were sexually assaulted over a period of several hours.
Mary-Ann was stabbed in the neck and her friend shot in the head.
Both girls were left for dead in the park.
But the 18-year-old regained consciousness and managed to flag down a passing motorist.