The acquittal of the teenage defendant in a high profile cybercrime case today is a setback for police that will have profound implications to the future of criminal prosecutions for computer crime in the UK, according to legal and security experts involved in the case.
Aaron Caffrey, 19, was cleared after a jury unanimously decided he was not guilty of unauthorised computer modifications related to the attack that crippled the Port of Houston's Web-based systems in September 2001. The jury of six women and five men reached its verdict after deliberating for just three hours.
Prosecution and defence in the case both agreed an attack that slowed the massive American sea port's Web systems to a crawl was launched from Caffrey's home PC. The debilitating attack on the Port of Houston's vulnerable NT-based systems was the result of a misdirected attack by Caffrey against a fellow chat-room user, the prosecution claimed.
But Caffrey, of Shaftesbury in Dorset, claimed the evidence against him was planted on his machine by attackers who used an unspecified Trojan to gain control of his PC and launch the assault.
A forensic examination of Caffrey's PC found attack tools but no trace of Trojan infection.
The case therefore hinged on whether the jury accepted the defence argument that a Trojan could wipe itself or expert testimony from the prosecution that no such technology existed.
Today's verdict shows that the prosecution case failed to convince the jury.
Speaking after the verdict, Caffrey said he angered by the accusations against him and at how he was "interpreted" by the police and portrayed in court. He was "delighted" to have been cleared but "very nervous and shaky".
Caffrey hopes to rebuild his life and look for a job in either computer security or programming.
Outside the court his barrister, Iain Ross, said: "He [Caffrey] has always insisted he was not guilty and that he was a victim of a criminal act rather than being a criminal himself."
Ross described the case as a setback for the police.
"How can the prosecution ever prove someone wasn't the victim of a Trojan horse attack? Trojan horse attacks can happen at any time," said Ross.
"The case is a setback for police in the prosecution of computer crimes," he added.
Neil Barrett, technical director of security consultancy IRM, who appeared in the case as an expert witness for the prosecution, agreed with this assessment.
"This is a setback because it opens the floodgates to Trojan arguments, not just in hacking cases, but in the prosecution of paedophile cases," Barrett told The Register.
"It's very difficult to counter the quite simple argument that someone else did it and ran away. We had hoped to showthat if someone else did it they would have left footprints and that, in this case, there weren't any."
"It's difficult to prove something hasn't happened," Barrett added
The case is likely to prompt a review by police of how evidence is put before a jury in computer crime cases, he added.
Parties on both the defence and prosecution side of the case floated the opinion that complex computer crime cases might better be tried before a panel of experts, rather than a jury. However juries are frequently asked to consider complex cases involving fraud. Also since changes in the rights of a defendant to trial by jury could only by authorised by Parliament this proposal is more a debating point than a practical suggestion.
Caffrey's case is the first ever in the UK decided by a jury under the Computer Misuse Act. But the Trojan defence has succeeded before in a British court. In April this year, Karl Schofield, 39, was cleared of possession of child porn when prosecutors accepted expert testimony that the unnamed Trojan could have been responsible for the presence of 14 child porn images on his PC. ®