David Ludwig's attorneys, meanwhile, said that videotape from surveillance cameras will show that the suspect did not kidnap the 14-year-old daughter of Michael and Cathryn Borden, who were gunned down in their home Sunday.
An 18-minute video recovered from a laptop computer in Ludwig's house shows him and another teenager taking guns from his house to another home and discussing using the weapons to "shoot and kill family members inside of the residence," court documents said.
It is not known whose house was targeted, but it was not the Bordens', investigators said. The court documents said Ludwig and Lohr abandoned the plan because there was too much traffic nearby.
Authorities described the video in an affidavit for a search warrant issued Thursday for the seizure of computer and video equipment.
Ludwig is being held without bail on murder and kidnapping charges after being flown back to Pennsylvania on Tuesday from Indiana, where he was captured by police. His girlfriend was with him when he was caught.
Police say Ludwig shot the Bordens at their Lititz home after an argument over his relationship with 14-year-old Kara Borden. The two had been dating, apparently secretly, friends and witnesses said.
Investigators have said that they are treating Kara as a victim — rather than a willing participant in the crime — but that the investigation is continuing.
Ludwig's attorneys wrote in court papers Friday that their client told them that the way he and Kara Borden acted at various stops on their 600-mile drive "will serve to negate" allegations he kidnapped her.
The filing by attorneys James Gratton and Merrill Spahn calls for investigators to preserve evidence such as receipts in Ludwig's wallet, so that surveillance video could be obtained. They also want information preserved from the teens' Web sites, cellular phones, computers and personal digital assistants.
Gratton read a statement to The Associated Press in which he said, "We want to make sure all evidence of exactly what happened here is preserved." He declined to answer questions.
A judge deferred action on the requests until Monday.
Kara Borden's lawyer, Robert Beyer, declined to comment on the filing.
About 100 people attended a prayer service Wednesday night at Monterey Chapel in Leola, where Michael Borden was a church elder who taught Sunday school.
"It was very poignant," Kellymarie Conlon, a friend of Kara's older brother James, told CBS News Early Show co-anchor René Syler.
Gregory and Jane Ludwig, David's parents, issued a statement Wednesday night, saying that no words can express "sorrow, shock and senselessness" of the shootings.