"Detectives investigating the London Bridge terror attack have carried out a search warrant at an address in east London in the early hours of Wednesday", police said in a statement.
Police said earlier that witness accounts suggested he might have been thrown into the river.
The body was recovered near Limehouse, downstream of London Bridge, at around 7.45pm on Tuesday by specialist officers from the marine police unit.
The force said formal identification has not yet taken place, but Xavier Thomas's next of kin had been informed.
Eight people died and 48 were injured in the attacks, including four unarmed policemen who had attempted to tackle the terrorists to the floor.
Ms Delcros is said to have been seriously injured. The latest arrests come on the eve of Britain's general election on Thursday, after a political campaign marred by the London attack and a suicide bombing in Manchester last month.
Wednesday's announcement comes as United Kingdom authorities face new questions over how one of the London Bridge attackers was let into Britain despite being on a security watch list.
In the footage, which was confirmed to be legitimate by the Metropolitan Police Service, a man can be seen fleeing one of the terrorists, who is swinging a knife at him.
A 27-year-old was detained on terrorism charges while the second, aged 33, was arrested on drugs charges.
Italian authorities said Zaghba had been stopped and questioned in Italy but had not been charged with any crime.
"We did everything we could have done, but there weren't elements of proof that he was a terrorist", he added.
The youngest of the attackers, an Italian national of Moroccan descent, he was allowed to enter the United Kingdom and had been living in east London.
Police have named the attackers as Khurum Butt, 27, who had been known for his extremist views; 30-year-old Rachid Redouane, also known as Rachid Elkhdar; and Youssef Zaghba, a 22-year-old Italian national of Moroccan descent who was reportedly working in a London restaurant.