May, under fire because of three major attacks in Britain in the last three months, said Corbyn wasn't fit to safeguard Britain's security at a time of heightened threat.
Police say the death toll from the attacks on Saturday night has now risen to eight. His girlfriend was also hit and seriously injured.
Abedi killed 22 people and wounded more than 100 when he detonated a bomb at the crowded Manchester Arena, where USA pop star Ariana Grande had been performing.
The Metropolitan Police said Butt had been subject to an investigation in 2015, but there had been no suggestion this attack was being planned.
Two of the men, aged 27 and 29, were held on suspicion of preparing acts of terrorism while the third was detained over suspected drugs offences.
Police arrested 12 people on Sunday in Barking, also in the east of the city, where both Butt and Redouane lived, but released all of them without charge.
Earlier this week, authorities identified the assailants of the attack as 27-year-old Pakistan-born British citizen Khuram B., 30-year-old Libyan-Moroccan national Rachid R. and 212-year-old Italian-Moroccan Youssef Z.
The families of the London attackers have condemned their actions on Wednesday, with relatives of Khuram Butt, Youssef Zaghba and the ex-partner of Rachid Redouane saying they were shocked at what had happened. However, authorities have yet to announce whether the attack was coordinated by the militant group's operatives in Iraq or Syria, or by a UK-based cell.