Jurors with the task of deciding the fate of alleged wife killer Gerard Baden-Clay have begun their deliberations.

The fate of alleged wife killer Gerard Baden-Clay now rests with a jury after a long-running trial that exposed the intimate secrets of his private life.

The seven men and five women retired on Thursday morning to consider whether the 43-year-old is guilty of murdering his wife in April 2012.

Allison Baden-Clay’s body was found on a creek bank at Anstead in Brisbane’s west on April 30, 2012 – 10 days after her husband reported her missing from their home in nearby Brookfield.

In Brisbane’s Supreme Court Baden-Clay pleaded not guilty to murder.

Prosecutors say the former real estate agent probably smothered his wife at their house and dumped her body where it was found under the Kholo Creek Bridge.

They say he was under significant personal and financial pressure after becoming entangled in a long-standing affair and running up large debts to support his struggling business.

The father of three vehemently denied the allegations during his trial, which ran for 18 days and heard evidence, including details of Baden-Clay’s multiple affairs, from 75 witnesses.

On Thursday, Justice John Byrne issued a stern warning to jurors after one downloaded material from the internet about how to approach jury deliberations.

He confiscated the document and warned them against seeking assistance from outside the court room, telling them they already had access to a guide to deliberations.

“You scarcely need to know what some overseas commentator speaking about a very different system of jury trials happens to think,” the judge said.

Jurors were told that to convict Baden-Clay of murder they must be satisfied beyond reasonable doubt of three things: that Allison was dead, that Baden-Clay killed her, and that he intended to at least cause her grievous bodily harm.

The judge has left it open for them to return a verdict of manslaughter, explaining that such a verdict related to unintentional killing.

Scratches seen on Baden-Clay’s face the day his wife vanished, and a trickle of Allison’s blood found in the couple’s car are among evidence prosecutors say proves his guilt.

His defence team suggested Allison drowned, or fell or jumped to her death, after taking an extra dose of anti-depressants and walking off during the night.

They pointed to her history of depression, and toxicology results showing elevated levels of an anti-depressant and alcohol in her system. Jurors deliberated for just over five hours on Thursday and will resume discussions on Friday morning.