"Perhaps the most crucial piece of evidence was the video," Morgan told the jury, adding that the girl appeared to have been drugged.
Melia's girlfriend, Heather Lewis, whom the prosecution identified as the adult woman on the tape, is accused of assaulting the minor and forcing her to be her sexual partner.
Melia's lawyer, Mark Catanzaro of Moorestown, said the girl appeared to be an adult and had consented to the sex act. There was no evidence Melia was even present at the taping, he said.
The two other girls Melia and Lewis allegedly assaulted lied to police to deflect criticism about themselves and their troubled families, Catanzaro said.
"They conjured up a story," he said.
Testimony before Judge Charles Delehey began after opening arguments, with some jurors looking away when the discussion became graphic.
Morgan warned the panel they would need to see explicit photographs and the 35-minute video police extracted from Melia's computer.
"I apologize for the disturbing material," he said.
Lewis, 36, of Pemberton, took the girls to Melia's home in Moorestown to be "exploited" for the couple's "sexual amusement and enjoyment," Morgan said. Police were notified after one of the girls told her stepfather.
The first witness to testify was one of the alleged victims. She said she occasionally visited Melia's house to babysit Lewis' son from a previous relationship. The child is her cousin, said the woman, who is now 23.
"I would go there to play with him, babysit him. He was attached to me. I spent a lot of time there," she said.
But one night she awoke in the house to find Lewis sexually assaulting her, she testified. When she tried to move away, Melia held her back, she said.
Police said that during a search of Melia's home on Cottage Avenue, they also discovered video of Melia engaged in sexual acts with calves on a Burlington County farm. He was charged with animal cruelty, but a judge dismissed the counts in 2009, saying there was no evidence the animals had been tormented by the acts.
Melia and Lewis are standing trial on more than 40 counts each of aggravated sexual assault, sexual contact, endangering the welfare of a minor, invasion of privacy, and other charges related to the teens.
When the girls gave statements to police in April 2008, they said the incidents had begun in 2000. They had difficulty pinning down exact dates or how old they were.
The girls, two of whom are sisters, said they were between 12 and 17 when they were assaulted, separately, by Melia and Lewis. They told police the couple used vibrators on them and forced them to engage in sex acts with the adults.
The charges carry prison sentences in excess of 52 years for each defendant, the prosecutor said. Melia also is charged with official police misconduct, and Lewis faces charges for allegedly sexually assaulting a 14-year-old boy and forcing him to have sex with one of the girls.
Lewis' public defender, Bonnie Geller-Gorman, said her client was not "the monster" the prosecutor portrayed her to be.
Before she moved in with Melia, Lewis lived with the uncle of the two sisters. Lewis and that man had a baby and she often invited the girls to Melia's house to babysit or to visit their cousin, the lawyer said.
She knew the third girl through family and neighborhood ties in Pemberton, Geller-Gorman said. When Lewis learned the girl had been impregnated by her stepfather, she suggested the girl notify police, Geller-Gorman said. Instead, the girl concocted a story about being assaulted by Lewis and Melia, the lawyer said.
"It's all lies to protect her stepfather," Geller-Gorman said.
Lewis and Melia were jailed after their arrests, then released on bail. Their trial is expected to last up to three weeks.
Contact Jan Hefler
at 856-779-3224, email@example.com, or follow @JanHefler on Twitter. Read her blog at philly.com/BurlcoBuzz.