The clue that could solve the disappearance of Jack O'Sullivan: Missing graduate's desperate mother begs public for help to find phone that could reveal why he has been missing for more than a month

Jack O'Sullivan's desperate mother has begged the public to help her find the one item that may reveal why her son has been missing for more than a month.

The 23-year-old law graduate vanished after going to a house party on Hotwell Road in Bristol in the early hours of March 2.

However, police said Jack's phone remained active for hours after he had last made contact with anyone.

His mother Catherine O'Sullivan said: 'It just doesn't make any sense.

'My appeal really would be if somebody picked up a phone for whatever reason or passed a smashed phone or anything, that would give us an indication of where that phone went.'

On March 2, the youngster met friends in Bristol for a normal Saturday night out, travelling by bus at 8.20pm from his village of Flax Bourton to a Wetherspoons pub in the city. 

At 10.45pm he texted his mother that they had moved on to a house party and safely arrived at the new location. 

'All good, keys are safe,' he wrote. At 1.52am he sent her a final text, saying he was OK. 

Shortly before 3am, Jack left the party alone.

CCTV captured some of his movements through the city from leaving the house party and passing the Junction Swing Bridge to finally turning down Brunel Lock Road at about 3.15am.

He called a friend who was still at the party at 3.24am. When the friend returned the call ten minutes later, Jack answered the phone and said 'hello' but nothing else. The call lasted for 58 second before being disconnected. 

Mrs O'Sullivan said the friend left the party soon after. 'She tried and tried to get hold of him but couldn't. She sent messages to him saying, ''Please let me know where you are, please let me know you're OK'' and ''please let me know when you get home''.' 

His family have now taken to walking his final route every day and at different times of the day just to try and experience what it might have been like for Jack, and any indication as to what could have happened. 

'I wanted to see if it was dark, and how it felt. But it's incredibly well-lit,' they said.

 Officers said his phone remained active on the Find My Friends app up until 6.44am.

Since then his parents have had to hear the heartbreaking news from the police that they are working on a hypothesis that he may have fallen into the river.

Jack's parents, Catherine and Alan O'Sullivan, have urged anyone in the Hotwells area on that date to come forward with information.

Mrs O'Sullivan says she wants 'the world to try and give them an answer' to where their son is, claiming it was 'very out of character' for Jack to go missing suddenly.

The couple also explained how 'heartbreaking' it was to celebrate their son's 23rd birthday on March 28 without him.

Mrs O'Sullivan told BBC News: 'I want the world to try and give me an answer to where Jack is. It's horrific.

'Jack's birthday was hell on earth and this last few days it's getting harder because the answers are just not coming.'

Jack's mother 'instantly' knew something had happened to him when she woke up just after 5am and realised he had not come home from the house party.

She said: 'We could only go by phone messages that we were getting on my phone from a family group chat and it was giving me a location in Hotwells as to where Jack was.

'So we go there and really nothing came to light, and here we are nearly 30 days after that moment with no further information or sighting.'

As she quickly realised her son was not home and using Find My Friends could see he was not at the location of the party, Catherine and her husband, Alan, immediately went out to search for Jack, in what would soon be the first of many days of 'hell'.

'We live hour by hour. You can't plan for the next day; we just communicate with police and we wait. We wait,' Ms O'Sullivan told the Telegraph.

Jack, who turned 23 on March 28, nearly a month after his disappearance, was described by his mother as sporty, determined and gentle. 

She said: 'He put tremendous amount of effort into his next steps. He had already secured summer placements which are really hard to get. But he put in 45 applications.'

She added: 'Jack is a really good chap. He's very gentle. He just wanted to make sure everybody else was OK.'

Ever since the night he disappeared, Jack's family have been out a number of times to retrace his last known steps.

Mrs O'Sullivan said: 'I was expecting it to be really dark and then to think well someone could trip but it's lit up like in the middle of the day.'

Avon and Somerset Police have appealed for anyone who was driving in the Cumberland Basin area, or who may have dashcam footage, to make contact. 

Police previously approached the family with a key that was found by authorities that they thought might have belonged to Jack, but it was not his. 

Senior investigating officer DI Jason Chidgey said officers had used drones, dogs and dive teams in the River Avon as part of a 'significant number of searches' in the area.

Detectives have also carried out extensive CCTV trawls and house-to-house enquiries, as well as looking at Jack's phone to work out why that was active after his last confirmed sighting.

However, Det Insp Chidgey admitted his team was still trying to establish Jack's movements following the last sighting of him on CCTV.

He said: 'This is an incredibly difficult and distressing time for Jack's family and friends and we are continuing our efforts to try and find him.

'The smallest bit of information could make a huge difference in our investigation so, even if you don't think it is important, we encourage people to still get in touch with us.

'We are keeping an open mind about where Jack is but this is very out of character for him and we have been working hard to track his movements that night.'

Mr O'Sullivan is described as white, about 5ft 10ins (178cm) tall, of slim build and with short, brown hair.

He was last seen wearing a quilted green/brown Barbour jacket over a beige woollen jumper, navy chinos and brown leather trainers with white soles.