Rt Rev Mike Hill also says he and many others are struggling to understand how anyone could ever do such a thing, and praised the Watt's family for acting "with dignity throughout".
Two churches in Bristol, St Ambrose in Whitehall and St Luke's in Barton Hill, are opening their doors today for mourners after body parts were found at a house in the Barton Hill area of the city.
A man and a woman are still being questioned by police on suspicion of Becky Watts murder. They were originally arrested on Saturday; police were granted extra time to question the pair.
Police must decide by this evening whether to charge or release the two murder suspects.
Five others are being questioned on suspicion of assisting an offender.
Bishop Mike said in a statement: "I feel sure that people both of faith and of no faith will join with me in wishing to support the friends and family of Becky Watts in the light of the deeply shocking and unfolding news of her death.
"They have acted with dignity throughout this awful nightmare since the day Becky went missing.
"Together with many people, I struggle to understand why there are people who can do such things to a young girl. As the father of four daughters this crime has affected me deeply. Becky's family are much in my thoughts and prayers at what must be an unbearable time for them.
"I am minded to be grateful to Avon and Somerset Police Service for their investigation of these heinous acts and hope that the truth of what happened to Becky will lead to both convictions and justice.
"May she rest in peace."
Listen to Rt Rev Mike Hill speaking to Premier's Marcus Jones on the News Hour:
Becky Watt's mother Tania, grandmother Pat and brother Daniel also said in a statement: "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.
"We are grateful to the police for all they have done and are continuing to do in this investigation.
"Whilst there are people in custody, none of whom are connected to the Watts family, we will not be making any further comment and we ask that our privacy is respected at this horrific time."
St Ambrose Church in Whitehall's doors are open from 10:30am today, whilst St Luke's Church in Barton Hill is open from 3:30pm to 5:30pm, and from 8pm until 9pm.
Rev Martin Gainsborough, from St Luke's, told Premier: "At a time like this, we feel it's absolutely crucial that the church rallies round and at the very least provides a focal point for people's grief and emotions and so on, a place of prayer.
"We want people to know that as a church, as a christian community, we are praying for this situation in all aspects.
"When people are grieving, when people are upset, they want to come together. It's how we hold on to our humanity, and I think the church can provide a forum for that... Standing alongside people in their grief and finding words, difficult though that may be, to speak into this situation."
Listen to Rev Martin Gainsborough speaking to Premier's Aaron James:
