Carers accompanying a disabled man on a trip to a Cambridgeshire zoo were 'on their phones' and 'ten metres behind him' before he allegedly hurled a three-year-old boy into a crocodile pit.

The boy sustained critical injuries at Johnsons of Old Hurst, near Huntingdon, Cambridgeshire, following the incident Thursday lunchtime.

The youngster is thought to have been tossed over the four-foot fence separating an aerial walkway from the enclosure below, where he landed on concrete before rolling into water.

He was attacked by at least one of the animals before hero zookeeper Tracey Johnson jumped into the pit and snatched him from further danger.

A man with learning disabilities was arrested at the scene on suspicion of attempted murder, but has since been bailed until September after being assessed as unfit for interview. 

Now witnesses have told how earlier they saw the man's carers 'on their phones' and not paying close attention during his trip to the zoo with other vulnerable adults.

A mother at the zoo at the time of the incident described hearing a 'loud scream' while sitting on a bench outside the enclosure.

She told the Sun: 'Someone later described the man that did it and said he was with carers.

'I don't know if it was definitely him but I saw one bloke of a bigger build, he had two carers with him and they weren't paying him much attention.

'If it was him, his carers were maybe ten metres behind him. They were English and chatting among themselves and on their phones.'

On Friday, Cambridgeshire police confirmed the boy is still in a critical condition in hospital, with his injuries said to include a broken arm and pelvis.

A spokesperson said: 'A three-year-old boy from Cambridgeshire remains in Addenbrooke's Hospital in a critical but stable condition.

'A 30-year-old man from Norfolk, arrested on suspicion of attempted murder, has been released on bail while detectives from the Major Crimes Unit conduct further enquiries regarding this incident. 

'The man, not known to the victim, was assessed as not being fit for interview.'

It is believed that the man was on a trip with other vulnerable adults and had at least two carers with him. 

Yesterday 55-year-old Mrs Johnson – whom one friend described yesterday as a 'special, steadfast, old-fashioned heroine' – was lauded as a hero after she climbed into the pen, waded to the boy and 'swooped down to pull him to safety'.

She is then thought to have escaped through a keepers' exit.

Chris Newman, director of the National Centre for Reptile Welfare, said: 'Her actions are nothing less than what I would expect of her. She is an incredible lady. It was a very brave thing to do.'

It was revealed on Friday that Mrs Johnson has just become a grandmother herself, with friends describing her as 'selfless' and 'always trying to help everyone'. 

Neither Mrs Johnson nor her husband Andrew, who run the zoo together, are under any illusions about the dangers posed by the crocodiles, as experts warned yesterday that if the boy had fallen on or near one of the creatures they would have bitten him on instinct.

Mr Newman said: 'I wouldn't expect them to eat a child, but they would bite if it landed on or near them. That's where the danger lies — they have such a powerful bite. Even an investigatory bite would be catastrophic.' 

Speaking on an episode of Farmer's Weekly in 2011, Mr Johnson said: 'When we're handling the crocs, the main thing we use is a pig board, and the idea is if you're sitting like this, he'll grab your leg and drag you in. 

'And just having the board in front takes away the striking point, the grip point, and they don't bother.

'The best way to build trust with them is not to stand up and look like you're the dominant person, but to get down to their level and work with them.

'They seem to accept you as one of the group. They definitely identify us as a family different to anybody else that comes in.'

Witnesses said Mrs Johnson sprinted into the enclosure and pulled the injured child away from the crocodiles to safety.

She and her shell-shocked husband were seen for the first time since the incident in exclusive pictures taken by the Daily Mail today as police sealed off the enclosure and spoke to staff. Friends said Mr and Mrs Johnson are 'mortified' by what happened.

Tearful witnesses described a blood-curdling scream from the reptile area at around 1.20pm on Thursday.

The boy had been on an elevated walkway watching at least 15 crocodiles and alligators when he was reportedly lifted over a 4ft safety fence and hurled about 15ft down into the enclosure.

He was then attacked by at least one crocodile, according to multiple sources. The enclosure houses more than a dozen crocodiles and alligators, including two large Nile crocodiles, Romeo and Cuddles, which measure between 9ft and 11ft. Romeo, the male, can weigh up to 485lb.

A mother who was at the zoo at the time said: 'We saw the air ambulance come over within about 10 minutes. They held up a white sheet in between the farm shop and the cafe so no one could see what was happening. 

'My daughter was oblivious. The little boy was only three and my daughter is two, it could have been her.' 

The Johnsons have said their 'thoughts and prayers are with the boy and his family'. 

A blog post on the zoo's website says the crocodiles were initially kept to help dispose of waste meat from the butchery, but they went on to be the start of a zoo.

The zoo is now home to more than 100 animals, including lions, tigers, sloth bears, capybaras and meerkats.