The judge threw out the case after the court had heard spectacular, even scandalous, evidence against Shrien Dewani, accused of arranging the honeymoon murder of his wife Anni.
The evidence, she said, was inadequate and 'riddled with contradictions'. Dewani walked free to head home.
The family of Anni Dewani condemned the decision, saying "we have not heard the full story". They said they felt "let down" by South African justice, and may take matters into their own hands with a private prosecution or an action for damages.
ITV News correspondent Steve Scott was in court:
A leading lawyer in South Africa has argued that the collapse of the trial of Shrien Dewani demonstrates the country's legal system can be trusted.
Eddie Classen, of BDK Attorneys in Pretoria, admitted the justice system was "not without flaws", but argued it was there not only to convict guilty people, but to acquit innocent ones.
The courts must be trusted. It is a cornerstone of any democratic society. This is a positive for the justice system. I would hope that this case and the [Oscar] Pistorius case re-enforce the belief in the effectiveness of the South African justice system.
Cleared honeymoon murder suspect Shrien Dewani "barely reacted" as a judge declared him not guilty of killing his new bride Anni in South Africa.
ITV News presenter Steve Scottwas in the courtroom to hear the decision:
Shrien Dewani - the British businessman put on trial in South Africa accused of arranging his wife's murder - is now a free man.
A judge in Cape Town dismissed the case, saying the evidence against him was 'riddled with contradictions'.
ITV News correspondent Richard Pallot reports:
The sister of murdered bride Anni Dewani has said the family have been let down by the South African justice system.
Speaking outside the court, Ami Denborg said the family's right to hear what happened to has been taken away, and they will be haunted for the rest of their lives by her death.
Prosecutors have said they still believe Shrien Dewani was involved in the murder of his wife Anni, despite a judge throwing the trial out of court in South Africa today.
Speaking outside court, spokesman for the South African National Prosecuting Authority, Nathi Ncube, insisted they had brought the case based on that belief.
He also denied that a "shoddy" police investigation was to blame for the trial collapsing.
It is unfortunate that Mr Dewani has been acquitted because we believe that he was involved.
The court did not find that he was innocent, the court said it could not rely on the evidence given by three witnesses who themselves had been convicted of the crime.
The judgment centres around evidence that was given by three people. Nothing has been said about the police, nothing was said about how the prosecution could have done better.
When you are dealing with witnesses who took part in the offence it is always going to be difficult to deal with those witnesses.
The family of murdered Anni Dewani have spoken in full of their "deep disappointment" after her husband Shrien was cleared of organising to have her murdered on their honeymoon.
Today we feel as a family that the justice system has failed us and we are deeply disappointed.
We came here looking for answers and we came here looking for the truth and all we got was more questions.
We waited patiently for four years to hear what really happened to Anni and to hear the full story of what happened to our dearest little sister.
All we wanted was to hear all the events and the hope of actually finding that out has kept us, as a family, going. Unfortunately we believe that this right has now been taken away from us.
Today we feel really, really sad, because we never heard the full story of Shrien. We heard that Shrien has led a double life and that Anni knew nothing about it.
And we just wish that Shrien had been honest with us and especially with Anni.
The knowledge of not ever knowing what happened to my dearest little sister...that's going to haunt me, my family, my brother, my parents, for the rest of our lives.
As she declared Dewani not guilty, Judge Jeanette Traverso warned the court she would not be swayed by public opinion.
The family of murdered bride Anni Dewani have spoken of their disappointment at seeing the trial against her new husband Shrien collapse.
They had previously publicly urged Dewani to reveal his version of events on the night she was shot dead.
Speaking as they left court, Anni's sister Ami Denborg said: "The justice system has failed us."
Cleared murder suspect Shrien Dewani is believed to have left the court in South Africa through a side entrance, without making a comment to the crowd waiting outside.
Supporters for both families clashed over the case after the judge dismissed the trial, with the Justice4Anni group again questioning Jeanette Traverso's role as presiding judge in the case.
The judge in the case against honeymoon murder suspect Shrien Dewani threw out the case today, saying the evidence presented fell "far below" the threshold demanded by law.
This is the moment she dismissed the trial: