Fourth man held in search for Wiltshire pensioner
The 24-year-old was held as police divers searched a stretch of the River Avon four miles from Mrs Guarino's home on the edge of Trowbridge in Wiltshire.
Earlier, divers made a "significant" find – believed to be bedding from Mrs Guarino's house – at a large pond in a business park on the other side of the town.
Police continue to question two men on suspicion of murder and have a deadline of this afternoon to either charge or release them.
A third man arrested earlier this week on suspicion of handling stolen property is still in custody.
The fourth man was arrested on suspicion of assisting an offender.
The two main suspects have been named as Marc Riley, Mrs Guarino's 24-year-old lodger, and his gay lover David Carr-Burstow, 19, both from Trowbridge.
Police divers spent much of yesterday searching a large section of the Avon in the hunt for the missing 61-year-old.
Following what police described as an "intelligence tip-off", divers were sent to a remote section of the River Avon in Bradford on Avon.
Police search teams cleared undergrowth from the banks of the river close to a golf course and the Kennet and Avon canal, while divers searched the chilly waters.
Neighbours said Mrs Guarino was a Good Samaritan, often taking in lodgers to supplement her income after she was forced to give up work because of a hip complaint which means she needs a stick to help her walk.
She was reported missing at the start of this week by her son and daughter, who live in Surrey. they were worried after not hearing from her for three weeks.
She was last seen at her doctors' surgery on January 7 while her Toyota Yaris car was left at a scrapyard in the town five days later.
Police have since cordoned off part of a landfill site near Calne, 15 miles away.
Forensic teams have been scouring the area of countryside known as Hilperton Gap, close to Mrs Guarino's home at Osborne Road in Trowbridge.
The discovery of bedding in a pond close to Virgin Mobile's headquarters in Trowbridge was described as "significant' for the case, which has been assigned more than 100 officers.
It emerged that Mr Riley had rented a room at Osborne Road from her since October last year.
A friend of Mrs Guarino, Sarah Jane Newbury, said: "I went on holiday with her and she took me to visit her son and daughter and she had a close relationship with them.
"I am certain she would contact me if she needed to as she always has before and her disappearance is very suspicious."
Neighbour Pat Baker added: "It has upset me enormously. She is a lovely lady. She is a little bit of an invalid and finds it difficult to walk anywhere."
Mrs Guarino's cat is being looked after by neighbours, while police activity in Osborne Road has continued.
The police helicopter has been using thermal imaging cameras over Hilperton Gap, as well as at other sites around Trowbridge.
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