Swaraj was speaking to reporters on Saturday at Vidisha, her constituency, about 50 km from Bhopal.
"A person cannot be held guilty merely on the basis of media reports or police action," she remarked.
Masood was found murdered in front of her house in the posh Koh-e-Fiza area in Bhopal on August 16 last year.
Singh is understood to have close relations with Masood as well as arrested alleged mastermind Zahida Parvez - an interior designer - which resulted in latter's resentment towards the activist, prompting her to order the killing.
Meanwhile, Youth Congress workers burnt an effigy of the BJP legislator in Bhopal on Saturday and demanded his expulsion from the ruling party.