Believe it or not, people do plead guilty to crimes that they haven't done, for a variety of reasons.
www.ipt-forensics.com/library/coerced.htm
www.economist.com/node/21525840
Also, some people come to believe that they have done something that they haven't done:
www.dailymail.co.uk/sciencetech/article-2913318
So, although it is possible that Vincent Tabak pleaded guilty because he actually was guilty, this is not necessarily the case.
He was on suicide watch in prison: he had never before been inside a police station, let alone on remand in a high security prison. We do not know whether or not he had a breakdown/was severely depressed/was under the influence of medication/was treated badly: all these scenarios are possible. He was also denied visitors for three weeks after being placed on remand.
By the time of the trial, he certainly gave the impression of being a broken man.
Although it is possible that Vincent Tabak pleaded guilty, this is not necessarily the case. There is very strong evidence that he did NOT plead guilty. The following evidence points to the a false plea obtained by tampering with the video-link.
(1) On 31st January 2011, Judge Colman Treacy "pencilled in" a date for the start of the trial, and also a date, 4th May 2011, for the defendant's plea and case management hearing at Bristol Crown Court.
http://swns.com/news/jo-yeates-murder-vincent-tabak-gets-trial-date-14737/(2) On 4th May 2011, a correspondent of mine who is resident in Somerset went to Bristol with the intention of sitting in the public gallery for the plea hearing. No such hearing was listed on the Crown Court timetable for that day, nor was there any clarification. My correspondent subsequently sat in the public gallery for several days of the trial later in the year.
(3) On 5th May 2011, the press reported that Vincent Tabak's plea and case management hearing was held at the Old Bailey, London - the only one of his hearings not to be held in Bristol. No explanation for the change of date and venue was published. The press had been tipped off about the changes, but the public had not been told.
(4) Instead of Judge Treacy, the hearing was held before Mr. Justice Richard Field, the judge who would also hear the trial. The defendant had not previously appeared before Judge Field, who would not be able to recognise Vincent Tabak. No explanation was published for the change of judge.
https://www.theguardian.com/uk/2011/may/05/joanna-yeates-neighbour-admits-killing(5) At this hearing, Mr Nigel Lickley QC made his second appearance as Counsel for the Prosecution of this defendant. As Vincent Tabak appeared only by video-link on both occasions, Counsel could not be held responsible if the person claiming to be the defendant were not the same person on both occasions.
(6) At this hearing, Mr. William Clegg QC made his first appearance as Counsel for the Defence of this defendant. He was instructed by Ian Kelcey, a different solicitor from the one who had instructed the barristers who had represented Vincent Tabak at the earlier hearings, from a different law firm. There is no evidence of Mr. Kelcey ever having been present at any of the hearings, nor is there any evidence of Mr. Clegg ever having visited Vincent Tabak in prison. So Mr. Clegg could not possibly say whether the person on the video screen at the Old Bailey was the real Vincent Tabak.
(7) Mr. & Mrs. Yeates were escorted by a police officer, Emma Davies, from Bristol to London for the plea hearing. Neither of them had ever met the defendant, so they could not be sure whether he was the person on the screen.
(8) Neither Greg Reardon, nor any of Vincent Tabak's friends, nor his family, nor Hilary Douglas, the only journalist who had interviewed Vincent Tabak, nor anyone else who would recognise him by sight, was reported to be present at the Old Bailey.
(9) After Mr. & Mrs Yeates got home, they told a journalist that they had expected Vincent Tabak to plead guilty. This was an admission that Emma Davies had told Jo's parents beforehand, and she could have known only if it were the police and prosecution who controlled the plea.
(10) When he heard about the plea, the Tabak family spokesman said he was shocked by the news and had heard no suggestion that a guilty plea would be entered.
(11) When he heard about the plea, Vincent Tabak's friend Joran Jessuran, a software engineer from Eindhoven University, tweeted that he had not expected that.
(12) DCI Phil Jones made a statement to the press outside the Old Bailey after the hearing. He was not reported to have been inside the courtroom. It is possible that he had met Vincent Tabak at the police station after he was first arrested, but he took no part in the prisoner's interrogation.
http://www.mirror.co.uk/news/uk-news/jo-yeates-neighbour-vincent-tabak-126826(13) The only evidence allegedly linking Vincent Tabak to the crime was enhanced DNA and 11 coat fibres on the victim's clothes, and microscopic blood traces from the victim in the boot of the car he used. He had no motive so his lawyers had no reason to allow him to plead guilty to killing her.
Just as an actress was engaged to impersonate Joanna Yeates in a TV reconstruction, it would have been straightforward to hire an actor resembling Vincent Tabak to impersonate him for the plea hearing. The room in which the actor sat could have been anywhere. Bristol is a centre of expertise for cartoon animation, so it is also possible that the plea was entered by a digital video simulation of Vincent Tabak.
