Mina Smallman, 65, is unhappy with the Met Police Commissioner’s response to poor policing and says it’s “time for her to go”.
Her daughters Bibaa Henry, 46, and Nicole Smallman, 27, were stabbed to death by Danyal Hussein, 18, at a park in Wembley, north London, in June last year.
Ms Smallman said the actions of the two PCs had taken her “to the depths of darkness of how on earth could you do that”.
She added: “Up until that point I had never imagined what the girls’ dead bodies looked like.
“But now and since then I have flashes of what I think that picture is.” On Dame Cressida, she added: “This is the woman who is going to tackle what we’re up against in the Met? I don’t think so now. No, it is time for her to go.”
Retired archdeacon Ms Smallman had previously said the embattled commissioner should remain in her post to rid the force “of the rot, once and for all”.
But she changed her mind after criticising Dame Cressida’s response to a police watchdog investigation into how the Met initially reacted when told the sisters had gone missing.
In a highly critical report published last month, the Independent Office for Police Conduct said the Met needed to apologise to the family of Bibaa and Nicole for failings in the way it handled the report that they had disappeared.
Ms Smallman said she had been asked “time and time again” if Dame Cressida should resign.
She said she was “so disappointed” by the Commissioner’s response to the IOPC’s report.
She added: “I said to myself, ‘If you need to be told to apologise by an organisation…’
“She knew it was true, she had all the evidence.”
Killer Hussein, who is said to have made a bizarre pact with a demon to kill women in return for a huge win on the lottery, has been jailed for life with a 35-year minimum.
The Met initially failed to launch a search for Bibaa and Nicole when the alarm was raised, it was said. Friends and family had to look for them and their bodies were eventually discovered by Nicole’s boyfriend.
As detectives launched a double murder investigation, two PCs slipped behind the police cordon to take pictures of the victims, who they are said to have described as “dead birds”.
Their six revolting photographs were then posted to a WhatsApp group of 40 police officers, who called themselves the “A Team”.
PC Deniz Jaffer, 47, and PC Jamie Lewis, 33, have admitted misconduct in a public office and will be jailed next month.
After the pair pleaded guilty at the Old Bailey earlier this month, Ms
Smallman said the Commissioner needed “to drill down and get the rot out once and for all”.
Asked at the time if Dame Cressida should resign, she had replied: “I do not think that is the right thing to do.
“Kicking people out does not fix the problem. Keep her in the position and get her to do the job.”
A statement from Met Assistant Commissioner Helen Ball said: “Our thoughts are with the family and friends and we deeply regret the additional distress this matter has caused them.
“We’re profoundly sorry personally and on behalf of the Met.”
Dame Cressida has weathered a storm of criticism in recent months and has resisted calls for her resignation, particularly following the Sarah Everard case.