Detectives were granted an extension of 36 hours to question the 20-year-old boyfriend. The second man, aged 26, is believed to be a friend of the boyfriend. Two other men arrested after the murder have been released on bail.
As the police inquiry expanded, relatives and friends in the Croydon area of south London struggled to come to terms with the killing. Ms Bowman was stabbed repeatedly as she returned home early on Sunday morning after a night out. She had celebrated her 18th birthday last week and was about to sign her first professional modelling contract. She had just returned from a holiday in Greece with her boyfriend.
Jessica, a schoolfriend who did not want to give her full name, told The Independent: "She was always getting all this stuff about how she was the next Kate Moss [also from Croydon]. Sally just wanted to be good at modelling. She had the looks, she is stunning." Stopping herself momentarily, Jessica added: "I mean, she was stunning."
Scotland Yard declined to comment on rumours that Ms Bowman had split up with her long-term boyfriend on Friday night after a row. They also refused to reveal whether Miss Bowman had been sexually assaulted or if her murder was being linked with her modelling career, which began in January this year when she approached a Croydon-based model agency.
Executives at her modelling agency, Pulse Model Management, said that although she had only taken part in unpaid catwalk events and private shows for new designers and students at London's two main fashion colleges Ms Bowman was destined for a successful career. Her last major show had been at the Café de Paris in Piccadilly, where she was approached by several central London model agencies.
Vasco Rodrigues, head of public relations for Pulse, which has 400 models, said: "Even as a 17-year-old, we knew she had what it takes. There are not too many girls out there who match what is wanted - she was 6ft, blonde, blue-eyed and a size eight, who could carry herself extremely well on the catwalk.
"She had already been getting lots of inquiries from big designers and fashion houses. We had a contract ready for her to sign."
Ms Bowman attended Croydon's School for Performing Arts before leaving at 16 for a hairdressing course at a further education college. She got a job as a junior stylist in a local salon, Blast Hair Design, in November. A former colleague said: "She was so excited about her holiday. It was her dream way of spending her 18th birthday."
Scotland Yard said they were still appealing for witnesses who could account for Ms Bowman's movements between 2am and 6.30am on Sunday, when her body was found.