Jonathan Laidlaw said prosecutors had produced "no smoking gun" to convict the former News of the World editor Brooks, who is accused of conspiring to hack phones, pay officials for information and obstruct a police investigation.
He accused prosecutors of constructing their case "not on direct evidence but around inference."
Seven people, including Brooks, her husband Charlie and her former colleague and lover Andy Coulson, are on trial over wrongdoing at Rupert Murdoch's now-defunct News of the World tabloid. All deny the charges.
Defense lawyers are making closing speeches at the long-running trial, which began in October. Judge John Saunders has told jurors he expects they will retire to consider their verdicts on June 9.
Murdoch shut down the News of the World in 2011 after evidence emerged that its staff had eavesdropped on the voicemails of celebrities, politicians and crime victims. Murdoch's News Corp. has paid millions in compensation to people whose phones were hacked.
The scandal soon ensnared the media, police and political establishments in Britain, where Murdoch's newspapers wield substantial political clout. Brooks was a friend of Prime Minister David Cameron and Coulson was the prime minister's former communications director.
Laidlaw said in the media coverage of Brooks, "opinions have been expressed with views running from criticism to comment, through inaccuracy and bias, to downright cruelty and vitriol."
"This case has been described as the trial of the century," he said. "Awful things have been said about Rebekah Brooks herself over the last few years."