“And then when she went off the bus, they thought that they’d failed and that maybe, perhaps there was something else they could have done.

“So to learn that actually, this baby had been dead the whole while and that her mother was sitting there knowing this was happening, that must have just been horrifying.

“Some of them said that they actually had the effects of trauma, unable to sleep, had to take medication because of it. It must have just been so distressing for everybody on that bus.”

Rosalin Baker, 25, had been known to social services for many years. She was an addict with a chaotic life and had been sofa surfing between friends and family.

She was in a relationship with cocaine and heroin addict Jeffrey Wiltshire, a rapper 23 years her senior who had fathered 23 children with 18 different women.

Katie Gibbons says: “Because of the age gap there must have been some kind of power imbalance between the two of them. Imani was born really prematurely, aged 28 weeks. And so she spent her first 64 days in, incubator under kind of intense supervision.

“When Imani was in the incubator, her mother didn’t visit as much as you would normally expect, Jeffrey didn’t visit once.

“And Rosalin wouldn’t tell social services what his name was. So he was very much not in the picture.”

When baby Imani was discharged from hospital, Rosalin went to stay with her grandmother in Essex.

But nine days before the bus incident she moved out and went to stay with Wiltshire in his Manor Park bedsit.

On the day Rosalin got on the bus, CCTV footage showed her with baby Imani on her chest in a carrier, and she was pushing a buggy.

Wiltshire gave her a kiss as she boarded and then a thumbs up.

She sat on the bus for about 20 minutes, texting on her phone before she raised the alarm that her baby was unwell and someone called 999.

“The other passengers all stepped in, and several of them tried to resuscitate Imani,” Katie Gibbons explains. “All the while, Rosalin was quite impassive, again looking on her phone, not saying anything to the extent that another passenger thought that one of the passers-by was actually the mother because she was so distressed.”

Even when paramedics arrived on the scene, Baker sat calmly texting on her phone, showing little emotion.

During her 2017 trial the prosecutor Duncan Atkinson QC said: “They (the passengers) were panicking and distressed. In contrast, Baker was noted to be cold and calm.

“As those members of the public, and then paramedics, sought to help her child, Baker sat to one side and sought to contact first her sister and then Wiltshire.”

Phone records later revealed she sent her sister a text message which read “Imani is dead sis x”.

But the paramedics quickly established that baby Imani had not died on that bus – her body was cold, she had been dead for some time.

And a postmortem revealed she had also suffered horrific injuries which were way beyond what would have been caused by attempts to resuscitate her.

Forensic scientist Jim Fraser explains:  “Babies don’t just die. There’s a reason why they die.

“What the postmortem in this case encountered was a whole series of serious injuries. I don’t think you need to be a pathologist to realise that when a baby has 40 rib fractures, a fractured skull, a subarachnoid (brain) haemorrhage and an injury to the brain stem, these are not accidental injuries. These are injuries that have been inflicted by someone, and they’ve been inflicted over a period of time.”

Doctors and police quickly realised that baby Imani had been subjected to chronic child abuse and they now had to find out who was responsible.

Former murder detective Gary Holmes says: “Poor Imani, who was only 16 weeks old at the time of her death, had been in an incubator for the first 64 days of her life. So effectively half her life had been hospitalised in a high dependency unit since birth.

“However, when we looked into the history of the parents  we found that Rosalin Baker only visited 16 days of those 64. So imagine that is your newborn baby, knowing that baby is very ill or very weak may not survive, and you only visit her 16 days out of 64. That was a level of concern.

“And the next level of concern was that there was a reluctance to name the father, who was Jeffrey Wiltshire. Wiltshire, by the way, had never visited Imani hospital for all their 64 days.

“So here, from the very, very inception, this inquiry, we could already identify that both parents seemed very, very distant from that child and her welfare.”

Tests proved that Imani had actually died up to 24 hours before her mother took her on the bus journey.

Rosalin Baker and Jeffrey Wiltshire were the prime suspects in the case – but police had to prove which one of them inflicted the injuries.

They were charged with their daughter’s murder – and they quickly turned against each other.

Baker claimed Wiltshire had been coercive and abusive towards her so when she woke up one day and he said he had killed Imani, she went along with his plan to cover up the killing out of fear.

Police dismissed that, concluding that she could have raised the alarm the moment she got on the bus and told the truth.

While Wiltshire simply denied any involvement in Imani’s abuse or death at all.

Criminal defence attorney Chalon Young Pfeifer says: “The public perception would be that it doesn’t matter who inflicted the death.

“Both of these people are responsible and it’s murder. However, legally speaking, without being able to prove an intent to kill the child or a cause of death, you cannot prove murder, that in itself being the difference between ten years in jail and spending the rest of your life in jail.”

The jury deliberated for 14 hours but in the end they couldn’t agree the evidence was beyond reasonable doubt for murder. Baker and Wiltshire were convicted instead of causing or allowing the death of baby Imani. They were jailed for 11 years, reduced to ten on appeal.

Gary Holmes says: “The person who I think it affected the most on that bus was the lady that administered CPR. And I spoke to that lady at length after she gave evidence and she gave evidence and she was from Italy.

“A lovely lady was just on her way to work that day. That lady was totally innocent.

“None of her business,  but she wanted to do the best she could. And when she discovered that this baby was cold as ice, as she described it, and then saw the bruise under the eye, and still had massive CPR, even though she might well have known that she was dead.

“But it was a horrific thing for her. She could not get on a bus again.

“She did want to travel on public transport again but if she saw a baby, she’d be upset because she was worried the same thing would happen again.

“And that’s the level of trauma that Rosalin Baker subjected this lady to.”

Katie Gibbons adds: “Looking back at this case, there’s so many parts of it that ignite different emotions – anger, frustration – but the overwhelming sense of this just pure sadness and pain you feel for this little girl who had nobody looking out for her.

“She didn’t have the love and support of her parents. Definitely. She didn’t have wider protection of social services. Probably the safest she had been was when she was in an incubator. And that’s just a really, really tragic start to any life.”