Detectives are questioning a 36-year-old man on suspicion of the murder of the London schoolteacher Sabina Nessa, in what they called a “significant development” in the case. The man was arrested at 3am on Sunday at an address in East Sussex and was taken into police custody. He is the third man arrested over the killing. DCI Neil John, of the Metropolitan police’s specialist crime command, said: “Sabina’s family have been informed of this significant development and they continue to be supported by specialist officers.” Nessa, 28, is suspected to have been killed as she made what should have been a five-minute journey on foot to a pub from her home at about 8.30pm on Friday last week. She was found dead the following day in Cater Park in Kidbrooke, south-east London, where on Friday about 500 mourners held a candlelit vigil in her memory. The killing has reignited concerns about the level of danger women face in Britain. Two men previously arrested by homicide detectives – a 38-year-old man and a man in his 40s – were released under investigation. Detectives have until the early hours of Thursday morning to question the latest suspect, before deciding whether to charge him or release him under investigation. The arrest on Sunday came 48 hours after police appealed for help to trace a man captured on CCTV images taken near where Nessa was found dead. Scotland Yard would not confirm if the suspect was the man in the footage, but it is understood investigators are no longer seeking him. The man in the CCTV images was filmed on the night of the killing carrying what is thought to be a reflective red item. Detectives have said the man may have been trying to conceal the item up his sleeve but that police retained an open mind as to whether it was used in the killing. A 12-second video released by the Met shows the balding man wearing a black hooded coat and grey jeans looking over his shoulder and pulling at his hood as he walks down a footpath. Police said they were content that neither of the two men previously arrested featured in the CCTV footage. Nessa’s sister, Jebina Yasmin Islam, issued a statement on Friday evening before a rally at the East London Mosque – one of many vigils that took place across the country. “There are no words to describe how we are feeling as a family at the moment,” she said. “We did not expect that something like [this] would ever happen to us. I urge everyone to walk on busy streets when walking home from work, school or a friend’s homes. Please keep safe.” She added: “I ask you to pray for our sister and make dua [supplication] for her. May Allah grant her paradise.” Nessa’s uncle Shahin Miah described his niece as “a kind and an open-minded person”, who was “always smiling and helping others”. He said her death had “once again brought to the fore the question of women’s safety on the streets”, adding: “We don’t want what happened to Sabina to happen to anyone else. We don’t want any other mother’s chest to be empty or filled with deep sorrow, or to see the tears in the eyes of any father.”