A spokesman for the Metropolitan Police said:
"All lines of inquiry were considered in the early stages of the investigation. The investigation was detailed and complex and officers had a duty to explore every avenue of inquiry and retain an open mind about the circumstances.
"They carried out numerous actions including door-to-door inquiries, leaflet drops, searches, interviews and forensic analyses.
"The CCTV evidence took some time to collate and analyse but then clearly showed a veiled suspect trailing the victim before the attack.
"Konye was arrested as the investigation progressed."
Ms Oni said officers were incompetent "to kind of accuse me of doing it to myself, when I've said somebody has followed me from my workplace to my home".
"I even got told that they watched the CCTV footage and they saw no-one following me," she said.
"We've all seen the CCTV footage. There was a person in a veil following me.
"Why was this not found in the beginning? Nobody has answers to tell me."
Naomi Oni, a Victoria's Secret shop assistant, was left scarred for life after suffering serious burns on her face and chest in the incident in Dagenham, east London, in 2012.
Her former friend, Mary Konye, 22, who disguised herself in a Muslim veil before throwing the sulphuric acid, was jailed for 12 years last week.
Ms Oni told the BBC Radio 4 Today programme that police were slow to act on information she gave them about the attack.
She said it almost felt like she had "been accused of lying", adding that she had suffered "pain and backlash for her (Konye's) actions and other people's incompetency".
The victim of an alleged acid attack has been given an award in honour of her bravery. Naomi Oni was left with severe facial burns after the incident in East London.
Since then she's been trying to rebuild her life - and last night she was celebrated at the Inspirational Awards for Women.
Naomi joined Lucrezia Millarini in the ITV studio today, along with the woman who helped to rebuild Naomi's face.
An acid attack victim has told ITV's Daybreak that it remains a mystery why a 15-year-old boy carried out the assault.
Tara Quigley, 28, said she answered the door to the teenager, a stranger, who asked to speak to "Michelle" just before 9pm on April 30.
She said: "I was at home with my family. A young man knocked at my front door, asked me if my name was Michelle, to which I told him my name was Tara, so he left, quite abruptly. He came back about five minutes later and knocked again - as soon as I opened my front door, he threw the acid at me."
The 28-year-old managed to shut the door after the attack and rinse her face with water while an ambulance was called.
The 15-year-old pleaded guilty to a charge ofthrowing corrosive fluid on a person with intent to do grievous bodily harm and is due to be sentenced on Friday, a Scotland Yard spokesman said.
A mum-of-two who was badly injured when acid was thrown in her face on her own doorstep has told Daybreak she "feels quite sorry" for her attacker.
Tara Quigley, 28, gave her first interview since acid was squirted in her face at her Romford home in May and dubbed the perpetrator "a child that is not capable of making an adult decision".
Kirstie Trup, the North London teenager who was attacked with acid in Zanzibar last month, has vowed to return to the island.
Kirstie and her friend Katie Gee, also from London, were targeted by two men on a moped while on a volunteering holiday.
Despite her ordeal she has insisted she has many happy memories of her spell in Zanzibar where the two childhood friends worked with underprivileged children.
"This experience, as horrible as it has been, has not deterred me from wanting to do more voluntary work in Zanzibar," she told the Sunday Times.
"In fact, I would even like to return to do more work there next year."
She suffered severe chemical burns to her shoulder and back from the attack. The girls were flown back to Britain for treatment at the Chelsea and Westminster Hospital immediately afterwards.
Police in Zanzibar have interviewed several people, including eyewitnesses, and are believed to have identified a possible culprit, but no one has been taken into custody so far.
A woman who had acid thrown in her face as she opened her front door in Romford, London says she does not understand why a stranger attacked her and is appealing for anyone who may know something to contact police:
A woman has been left scarred for life after having acid thrown in her face by a stranger as she answered her front door in Romford, London.
It is believed Tara aged 28, answered her door shortly before 9.00pm on 30 April to a man asking for someone called Michelle.
A short time later, the man returned and when Tara answered the door he squirted an acidic substance in her face.
The victim managed to close the door and rinse her face with water as she called an ambulance.
Tara was taken to an East London hospital then transferred to a specialist burns unit where she remains in a stable condition.
Police have released an e-fit of a man they wish to speak to in connection with the acid attack.