THE stepbrother of missing Bristol teenager Becky Watts has been arrested on suspicion of her murder.

Nathan Matthews, 28, was held alongside his 21-year-old girlfriend Shauna Phillips by detectives investigating the disappearance of 16-year-old Becky in Bristol.

The couple, who live in Cotton Mill Lane in the Barton Hill area of the city, are thought to have been arrested on Saturday on suspicion of kidnap and later re-arrested on suspicion of murder.

Detectives had until this afternoon to either release or charge the pair but a police spokesman said today that officers had been granted a further 24 hours to question the four men and one woman arrested.

"The four men, aged 29, 29, 23 and 23, and one woman, also aged 23, were arrested on Monday evening," the force spokesman said.

"Today the district judge, sitting in Bristol Magistrates' Court, granted a warrant of further detention for an additional 24 hours. The five suspects remain in custody at this time."

The teenager, described by her relatives as "wonderful", vanished from her home in Crown Hill, St George, in the city, on February 19.

Wiltshire officers were among those who were drafted in to help find her.

Body parts were found at a house in Barton Court, in the Barton Hill area of the city, yards from the home of Mr Matthews and Ms Phillips, which has also been examined by forensic experts.

Earlier, Avon and Somerset detectives revealed that a further four men, two aged 29 and two aged 23, and a 23-year-old woman, had been arrested on suspicion of helping an offender.

Members of Becky's father Darren's family have identified Matthews as the son of his wife Anjie.

Becky's brother Dan Galsworthy wrote on Facebook: "To everyone messaging and supporting me I haven't replied to any messages because I simply have no words, I thank you all and deeply appreciate everyone's support. Love to you all."

Aunt Sarah Broom wrote: "So today my brother got his baby girl back - 12 days of pure hell filled with heartache.

"He is completely and utterly broken and there is nothing in this world of comfort to him - how does a parent ever recover from this? How can a family?

"So with tears rolling down my face, Becky you beautiful beautiful soul, you have touched so many hearts and changed so many lives.

"Your shy inverted nature has outshone and touched a whole city and beyond. You do not leave behind a legacy of anything other than pure heartfelt love and you, you beautiful girl, will live on forever in the hearts of all those that have carried you in theirs the last 12 days and of course those that carried you in your lifetime.

"Love each of my incredible family, we're all so crushed and drained of all we own for today but you bet next time we need to be strong we will be right there standing strong together, not for us but for someone who's changed and impacted our lives forever."

Becky's father and stepmother earlier said: "To receive such news as we did today about our dear daughter and stepdaughter Becky is too much to bear."

The teenager's mother Tania Watts, brother Daniel and grandmother Pat said: "We are devastated to be told of this latest development. We are at an utter loss to understand why anyone would want to hurt our beautiful Becky in such a brutal way."

They added that none of those in custody is "connected to the Watts family".

John Galsworthy, speaking on behalf of the Galsworthy family said: "Becky was a wonderful daughter, sister, granddaughter and niece and we cannot put into words how devastated we are."

The search since Becky was officially reported missing on February 20 has involved a social media campaign which has reached more than four million people worldwide.

Police said formal identification procedures of the body parts have not yet been completed.

Floral tributes have been left close to the site of the discovery, and also at the gates of Becky's home.

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.

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.

Later, it emerged that Ms Phillips had been taken to hospital by police after falling ill.

An Avon and Somerset Police spokesman said: "We can confirm that the woman in custody arrested on suspicion of the murder of Becky Watts was taken to hospital last night after feeling unwell in custody.

"She was seen by a doctor and taken back into custody a short time later."

There was a heavy police presence in the Barton Hill area as uniformed officers continued fingertip searches of the area surrounding Barton Court and Cotton Mill Lane.

Forensic experts were also continuing their examinations of two houses in Barton Court and neighbouring Cotton Mill Lane.