Investigators found “multiple counts of fraud” on Biffle and Grossu’s bank accounts, according to the warrant, which stated, “This fraud appears to have been a strategic and coordinated strike against all accounts through multiple States which has resulted in hundreds of thousands of dollars being stolen.”

Authorities said that “multiple conspirators” needed to have access and “intimate knowledge” of the Biffles' accounts, including their personal information like social security numbers, birthdays, passwords and more, to pull off the alleged heist.

Through multiple search warrants, investigators determined that those in the Biffles' “inner circle may have been involved in the stealing of large sums of money from the Biffles’ accounts.”

The warrant alleged, “This leads the affiant to believe that a conspiracy has been in place for a long period of time to commit fraud against the Biffle family.”

“Suspicious activity” on the family’s email and bank accounts started the day after the plane crash, the warrant said, adding, “Email addresses to accounts were changed, as well as phone numbers and passwords.”

As for the Jan. 7 break-in, the detective also said that the intruder spent “an extended amount of time inside the home.”

While no one has been arrested in the case—which is ongoing—the warrant said that sheriff’s investigators had matched features of a person seen in surveillance videos from the break-in to a woman they saw at Biffle’s celebration of life on Dec. 16. The woman was a friend of his wife Cristina Grossu’s, according to the warrant. 

E! News has reached out to Iredell County Sheriff for comment but has not heard back.

Following the Dec. 18 plane crash in North Carolina—which in addition to Biffle and his family also claimed the lives of three more people on board—Biffle and Grossu’s families spoke out on their tragedy. 

“We are devastated by the loss of our loved ones," read a joint statement from the families published by NASCAR at the time. "This tragedy has left all of our families heartbroken beyond words."

Biffle’s daughter Emma—who the 55-year-old shared with ex-wife Nicole Lunders—was remembered as "a wonderful human being with a kind soul who was loved by many people," while Ryder "was an active, curious and infinitely joyful child."

For a look back at the family’s life together, keep reading.