Jonathan Green, of the IOPC, said its investigations raises “very serious question” about the how the officer may have handled a “crucial piece of evidence”.“Undoubtedly the escalation in acid attacks is alarming and Londoners will expect that the Metropolitan Police Service treat all reported incidents of such attacks seriously and to investigate them thoroughly,” he said.“Our investigation will be rigorous in challenging how this evidence relating to the circulation of CCTV images was handled and seek to uncover whether other victims of crime may have been impacted upon as a result of any shortfalls.” After Webster was jailed for the manslaughter of Ms Rand, a charge he admitted, it emerged he was a member of a ‘drill music’ rap gang called 12 World.It was believed Webster, known as “The General”, had been himself attacked with a corrosive substance, as well as being stabbed and hit on the head with a baseball bat. Jacqueline Joiner, Ms Rand’s sister, said on behalf of the family: “We are deeply upset and disappointed. This [IOPC investigation] was hard news to hear as we are all still struggling to cope with the loss of Jo.“Had this acid attack in March 2017 been investigated properly at the time, Webster, the alleged perpetrator, would have been dealt with and may not have been free to carry out the horrific attack in June 2017 on Jo, and she may still be with us. We feel let down by the Metropolitan Police.”An IOPC spokeswoman said the officer, who has not been named, is being investigated for gross misconduct for alleged breaches of professional standards relating to his duties and responsibilities, orders and instructions and discreditable conduct. The police watchdog is not investigating allegations of a criminal nature.She added that after the detective obtained CCTV footage following the March 2017 attack, he updated the crime report saying “the images would be circulated when he was next on duty.”It is alleged they were not circulated until November 6, last year. That month, Scotland Yard’s Directorate of Professional Standards received allegations of misconduct and reported it to the IPOC. The officer is on restricted duties. Xeneral Webster has been jailed for 17 years Ms Rand’s family added: “We feel very concerned for the lady who was the victim of this attack. We know some of what she may be going through as we saw all of the pain and suffering that Jo went through.” A detective is being investigated over claims he sat on evidence which allowed a gangland killer to carry out the UK’s first ever fatal acid attack.The family of Joanne Rand, a mother of three who died after Xeneral Webster splashed sulphuric acid on her, said they felt “let down” the Metropolitan Police may have missed a vital opportunity to prevent her killing.The Independent Office for Police Conduct (IOPC) is trying to establish why an officer failed for 20 months to circulate CCTV footage apparently showing Webster launching a similar acid attack just months before he went on to kill.The pictures were obtained by the detective constable shortly after a woman was left with “significant hand and leg injuries” in an attack in north London in March 2017. It is alleged those images were released only in November last year, leading to Webster being identified as the assailant in just three day.By then, the 19-year-old gang member had been jailed for 17 years for the manslaughter of Ms Rand in June 2017. She was sprayed while an innocent bystander by Webster’s high strength acid in Frogmore, High Wycombe.The bottle of corrosive liquid was knocked from his hand during a row about a bike with another man. Xeneral Webster riding away from the scene of the acid attack on Joanne Rand in Frogmoor, High WycombeCredit:PA The 47-year-old carer for dementia patients suffered horrific burns and died 11 days later from multiple organ failure after contracting septicaemia from her injuries. Joanne Rand sustained multiple burns from the attackCredit:PA Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.