By Peter Bowes
BBC News in Santa Maria, California
The prosecution in the Michael Jackson child abuse trial has built a case on the theory that Michael Jackson could be a serial paedophile.
Monday's ruling could prove to be a turning point in trial
In a hearing on Monday, prosecuting attorney Tom Sneddon successfully argued that the jury should be told about at least two cases in the 1990s, where the singer was accused of molesting young boys.
The most widely reported case involved a teenager, Jordan Chandler, who said he was abused by the pop star in 1993.
At the time, Mr Jackson settled the matter out of court.
He vehemently denied anything improper ever took place and later said he chose to pay the boy a "considerable sum of money" to avoid being subjected to a "media circus" at a trial.
The agreement, which included a clause that neither party would discuss the matter publicly, reportedly involved a payment of $26m. No criminal charges were ever filed.
Documents which are understood to be Jordan Chandler's sworn declaration, a graphic account of alleged sexual encounters with Michael Jackson, have since been published on the internet.
California law allows the presentation of evidence of previous alleged acts of sexual abuse even if they were not prosecuted at the time.
Tom Sneddon argued for past allegations to go before the jury
The fact that a previous alleged victim may have entered into a confidentiality agreement does not prohibit him from testifying in a new criminal case.
"If the prosecution can get in any of this evidence their chances of convicting Michael Jackson increase almost astronomically," said Ms Bremner.
"Such testimony is often described as propensity evidence," explained Gloria Allred, a Los Angeles lawyer who briefly represented Jordan Chandler.
According to Ms Allred, the law allows the court to consider whether a defendant has a "propensity to commit acts of child sexual abuse".
"It is sometimes described as an MO, a modus operandi, a pattern of behaviour."
The prosecution will use such evidence to back up and give credibility to Gavin Arvizo's claim that he was abused by the singer in 2003.
They will attempt to expose similarities between the nature of the current allegations and those from a decade ago.
Past case: Gloria Allred represented Jordan Chandler
Before announcing his decision to allow previous allegations to be used in evidence, Judge Rodney Melville acknowledged that he had wrestled with the issue.
He told the court he had presided over another case where he allowed the jury to hear evidence of "prior acts" only to discover that the earlier allegations were far more serious in nature that the matter then before court.
The jury's view of the defendant was tainted and that case ended in a mistrial.
"It was a very important day in the case," said Ms Allred. "I think the court has made the right ruling.
"It was the intent of the legislature to allow accusations of child sexual abuse by prior alleged victims, even where those accusations never resulted in a criminal prosecution and never resulted in a civil trial."
Ms Allred said the prosecution would seek to prove that Michael Jackson is a serial abuser of children and that he achieves his goal by "grooming" youngsters.