An 18-year-old has been arrested in south London on suspicion of the murders of Bibaa Henry and Nicole Smallman.
He was taken into custody where he remains.
Detective Chief Inspector Simon Harding, who is leading the investigation, said: "Given the significance of this development, we visited the family in person today to inform them of the arrest. Our thoughts remain with them at this very difficult time.
"A team of forensic officers have been a constant presence at the park over the last few weeks carrying out meticulous fingertip searches at what is a vast and complex crime scene. Whilst that work has now concluded, smaller searches in outer areas of the park will continue. To date officers have recovered more than 1,000 exhibits - including property belonging to both Nicole and Bibaa, collected hours of CCTV and visited hundreds of homes and businesses. And those enquiries remain ongoing."
Bibaa and Nicole's mum Mina Smallman, a former Anglican archdeacon, spoke this month about her horror at losing her daughters and then hearing police officers allegedly took selfies with her dead daughters, saying they "dehumanised our children".
The family then started a petition to charge the officers accused. Two have been suspended.
Police believe Bibaa and Nicole were stabbed to death in the early hours of Saturday 6th June at Fryent Park in north London where they had spent the evening celebrating Bibaa's 46th birthday.
Police were called to the park on Sunday and they were pronounced dead at the scene and a post-mortem examination gave the cause of death for both women as stab wounds.
After the murder the family said in a statement: "Faith and prayer is keeping us going. I'm not sure how we'd get through this without it."
Police are appealing for people to come forward if they have any information.
People from the group they were with are believed to have left throughout the evening and by around 12:30am only Nicole and Bibaa remained.
The last contact they are believed to have had with family and friends was just after 1am and they were in good spirits and taking selfie pictures, listening to music and dancing with fairy lights until at least 1:13am. However, calls to the victims at around 2:30am went unanswered.
Anyone with information regarding the incident is asked to call the incident room on 020 8721 4205, via 101 or tweet @MetCC quoting CAD 3160/7Jun.
Information can be provided with anonymity to the Crimestoppers on 0800 555 111 or via crimestoppers-uk.org.