Nathan Matthews, 28, and Shauna Phillips, 21, are reportedly being held by police over the 16-year-old's murder, but police must either charge or release them by this afternoon.
A third man has been arrested in connection with the murder of 15-year-old Alan Cartwright, who was stabbed to death in Islington, north London, as he rode his bike with friends.
A 21-year-old man was arrested this morning at a property in Camden, the Metropolitan Police said. He is in custody at a police station.
Earlier today an 18-year-old man and a 17-year-old boy were arrested on suspicion of murder and remain in police custody.
The murder of Russian opposition politician Boris Nemtsov had a "political subtext", President Vladimir Putin has said.
In a speech at a meeting with interior ministry officials, Putin - who often came under criticism from Nemtsov - said the country should be "freed" of such killings.
Pc Toby Rowland, the police officer at the centre of the notorious Downing Street "Plebgate" incident, has accepted £80,000 damages in settlement of his libel action against former Government chief whip Andrew Mitchell, a High Court judge was told today.
Churches in Bristol are also planning to be open for people to pray or light a candle to remember the 16-year-old.
Rev Martin Gainsborough said St Luke's Church in Barton Hill would open this afternoon.
In a Facebook post, he said: "In light of the tragic turn in events concerning Becky Watts, St Luke's Church Barton Hill will be open for prayer on March 4 from 3.30pm to 5.30pm and 8pm to 9pm.
"There will be opportunities to light a candle, write a prayer, or just chat over a cup of tea or coffee."
Meanwhile, St Ambrose Church, which is close to Becky's home in St George, will be open throughout the day for people to light candles in the teenager's memory.
People have already begun laying flowers and cards near the scene of where body parts were found yesterday.
One card read: "Becky, we didn't know you but you are still in our hearts."
A 91-year-old political campaigner will stay on a database covering 'extremist' activities after police chiefs won a legal battle at the UK's highest court.
John Catt, from Brighton, wanted details about his attendance at various demonstrations by protest group Smash EDO removed from the database.
He won an appeal in 2013 after arguing that his inclusion on the database breached his human rights as he had not committed any crimes.
The Court of Appeal ruled that while some Smash EDO members were known for violence and criminal behaviour, Mr Catt had not been convicted of any crimes.
But Supreme Court judges today overturned that decision by a majority of four to one.
The head of the Russian security service, FSB, said they have identified "several suspects" in the murder of opposition politician Boris Nemtsov, according to the TASS news agency.
Open Kremlin critic Nemtsov, aged 55, was shot four times in the back as he crossed a bridge in Moscow last week.
Thousands of people attended his funeral yesterday.