Heather Mack, 19, and her boyfriend, Tommy Schaefer, 21, were found guilty in last year's killing of Sheila von Wiese-Mack in Bali.
Mack got a decade in prison while her boyfriend got 18 years. Federal authorities arrested the latter's cousin Wednesday.
The pair got tips on how to kill from Schaefer's cousin who lives in Chicago, according to a criminal complaint unsealed in federal court Wednesday.
Robert Ryan Justin Bibbs, 24, has been charged with conspiring to kill Mack's mother. He allegedly sent the tips while in Chicago.
Bibbs knew of the plot to kill beforehand and even gave the couple tips on how to avoid detection by law enforcement, according to the criminal complaint.
He did so to get money from the victim's estate through his cousin, the complaint alleges.
"He believed that Schaefer would gain access to Von Wiese's estate through the victim's daughter," it said.
Body stuffed in bag
The mother and daughter allegedly departed for Bali on August 2 last year.
Ten days later, the complaint alleges, the daughter's boyfriend followed and later joined them at the same resort .
Within hours of his arrival, his girlfriend's mother was bludgeoned to death, and her body stuffed in a silver suitcase, the complaint said.
The beaten body was found in the suitcase
that the couple had loaded in a waiting taxi outside the resort.
They had told the driver they'd be back soon, but after a long wait, he alerted hotel staff who noticed blood and called police.
The lovers were arrested the following morning at a nearby hotel.
Schaefer claimed he killed his girlfriend's mother in self-defense after a violent argument erupted over the couple's relationship. He told the court his girlfriend's mother started strangling him during an argument in the hotel room.
Her denied the murder was premeditated.
Mack told the court her mother had threatened to kill the couple's unborn baby.
The couple initially claimed they'd been briefly taken captive at the resort by an armed gang, whose members killed Mack's mother.
They later switched stories to self defense.