Since his death, his mother Melanie has been trying to get justice for her son, whom she says was let down by the Trust.
She says his death wasn't investigated properly, his care plan wasn't written until after his death, his claim of rape wasn't taken seriously, he was badly treated and his safety was at risk.
Today, the Parliamentary Health Service Ombudsman agreed with all her points and ordered a government review into his case.
She is of course pleased but says she won't rest until there's a public inquiry into the former North Essex Partnership University Trust (NEP).
The Parliamentary and Health Service Ombudsman had been looking into the deaths of two young men at the Linden Centre in 2008 and 2012.
The findings are damning and pretty shocking. It found there was "systemic failure to tackle repeated and critical failings over an unacceptable period of time", that there were 'missed opportunities' to ensure the safety of the men and that "the lack of timely safety improvements following their deaths is completely unacceptable and it's important the NHS understands why this happened and what lessons can be learned to prevent the same mistakes happening again".
When investigating the death of Matthew it found his management of risk 'was not rigorous enough', that his care wasn't adequately planned, the Trust didn't take adequate care of his physical health, they weren't open and honest with his family and the list goes on.
I spoke to Matthew's mother yesterday. She told me what a fun and happy young man he had been.
When he was sectioned she said he texted her and wrote "Mum, I'm in hell. Get me out of here".
Her reaction was to calm him down and tell him he was with the professionals and she's visit him soon.
But Melanie was told not to visit him for a week, to let him settle on the ward; the next time she saw him "he was dead on a trolley and I'm being told no, you can't touch..he's a crime scene and yet they didn't treat him as one, it was just a total mess".
She says the staff were buffoons.
The Ombudsman, Rob Behrens, is equally critical of the Trust.
He told me it was an extremely concerning report, that there was a catalogue of failings that were entirely unacceptable.
He said it was deeply worrying that changes hadn't been made at the Trust despite recommendations made by the Care Quality Commission and perhaps most telling was that he was "deeply disturbed but not surprised."
I asked him why he wasn't surprised... he said there is a structural issue in England with mental health and the human rights of young people in care units that needs to be addressed.
I write all this because rarely I have I done an interview with someone in a position like Mr Behrens who is so critical, so damning of a health Trust.
He says he would fully support a public inquiry, if NHS Improvement recommends one, and in fact would like to have investigated further himself, had he had the powers.
The NEP Trust has now merged with South Essex Partnership to form the Essex Partnership University NHS Foundation Trust.
Today, they apologised to the Leahy family, saying: "We will carry out the Ombudsman's recommendations and will support NHS Improvement's forthcoming review into the former NEP in every way possible."
Although this report focuses on the Trust in Essex, Mr Behrens says such failings in mental health are not confined to one area.
He says there is evidence it's happened before and still happens in many Trusts all across England.
He says the Government fully admits that good care comes down to good leadership, and in most cases he's found it's the leadership that's the problem. He wants this addressed as a matter of urgency.
Melanie Leahy's fight does not stop here. She insists the truth about her son's death will come out and she won't stop until it does.