James Lee DiMaggio "tortured and killed his best friend's wife and 8-year-old son," before kidnapping the friend's daughter, Hannah Anderson, and taking her out of state, according to search warrants that were unsealed Wednesday.
DiMaggio also "shot and killed the family dog," the warrants added.
Hannah Anderson was kidnapped on Aug. 4 by DiMaggio, 40, after she, her brother, Ethan Anderson, and her mother, Christina Anderson, 44, went to his Boulevard, Calif., home.
"He told us he was losing his house because of money issues so we went up there one last time to support him, and to have fun riding go karts up there but he tricked us," Anderson wrote in response to questions about her ordeal on the social media site ask.fm.
She wrote that DiMaggio tied up her mother and brother in his garage. Their bodies, along with a dead dog, were found after a fire at the home.
Authorities said that Anderson did not learn of her mother and brother's deaths until after her rescue, when an FBI forensics interviewer told her the news.
"I wish I could go back in time and risk my life to try and save theirs. I will never forgive myself for not trying harder to save them," Anderson wrote.
Funeral services will be held on Saturday, August 24 at Guardian Angels Catholic Church in Santee, Calif.
Anderson was rescued in Idaho on Saturday after FBI agents shot and killed DiMaggio.
Calls Between Hannah Anderson and James DiMaggio
Search warrants also revealed that both Hannah Anderson and DiMaggio's phones were shut off around 4 p.m. on Aug. 4 -- the day of the kidnapping and fire at DiMaggio's home.
At 4 p.m., Anderson was picked up from cheerleading practice at Sweetwater High School, but it is unknown who picked her up, according to the warrants.
Phone records showed that 13 phone calls were exchanged between DiMaggio and Hannah Anderson before the phones were turned off.
Authorities have said DiMaggio may have had an infatuation with the teen, and she wrote that she had been uncomfortable around him in the past but did not say anything because he was a family friend.
"He said it was more like a family crush like he had feelings as in he wanted nothing bad to happen to me," she wrote.
A friend told investigators during an interview that the two had taken multiple day trips together, including a recent trip to Malibu and Hollywood.
DiMaggio's sibling, Lora Robinson, made multiple calls to DiMaggio's phone on the day of the crime, according to the warrants.
Hannah Anderson Speaks Out on Social Media
Hannah Anderson's kidnapping on Aug. 4 set off a six-day manhunt that spanned several states until her rescue in the Idaho wilderness last Saturday.
Two days later, after her father made a public appeal for privacy, the teen began answering questions on the social media site ask.fm about how she couldn't escape, was denied food and "basically" stayed awake the entire time.
Anderson suspended her account, which had the username hannahbanana722, this afternoon. A source briefed on Anderson's case confirmed to ABC News that the posts made on the site were from the teen but was unable to confirm any of the information the teen shared.
A tip from a group of horseback riders led to the rescue of Anderson at a remote camp spot near Morehead Lake, Idaho, about 75 miles north of Boise, Idaho.
"They were extremely quiet. Didn't want to engage in any kind of conversation, kind of had a bad look on their face," Mark John, one of the horseback riders and a former sheriff's deputy from Gem County, Idaho, told "Good Morning America" earlier this week.
Anderson wrote that she remained calm when she saw the horseback riders because she was afraid DiMaggio would kill them.
When the group returned home the next day and saw the report of the amber alert for Anderson, they notified authorities.
Authorities located a blue Nissan, owned by DiMaggio, covered in brush on Friday.
Anderson wrote that DiMaggio forced her to help him cover the car with branches.
Aside from answering questions about her ordeal, Anderson responded to well-wishers from around the world and thanked them for their support.
She also posted a photo of herself in bright yellow shorts and said she got her nails done on Monday -- pink for her mother and blue for her brother.
The Associated Press contributed to this report.