Dale Cregan stood in the dock at Preston Crown Court, along with nine other defendants as the six women and six men chosen by ballot for the jury swore an oath on the Bible to give them a fair trial.
The 29-year-old is accused of the murders of David Short, 46, and his son, Mark, 23, in the months before allegedly killing Constables Nicola Hughes, 23, and Fiona Bone, 32, in an attack on September 18 last year.
Cregan's co-accused are variously charged with helping or taking part in one of the four murders or attempted murders, firearms offences or assisting an offender.
About 150 police officers, some armed with machine guns, are on security duty for the trial.
After the jury were sworn in, the judge, Mr Justice Holroyde, QC, said the trial, expected to last at least 10 weeks, would start properly on Thursday,. The jury were excused until then.
Before they were sent home Mr Justice Holroyde ordered them not to try to research the case on the internet, not to comment or seek comment on Twitter or Facebook or speak to anyone about the case – even family.
"You are duty bound to decide the case only on the evidence heard in court," he said and warned them if anyone was to disobey his orders "consequences could be serious".
He added: "There's quite a lot of police officers around this building and you may have seen reports in the media about security arrangements for the trial.
"I don't suppose it came as any surprise to you, there are security arrangements for a substantial trial like this. You must not in any way hold it against any of the defendants that these sort of arrangements are made."
The hearing was adjourned until today.