Federal agents in Chicago are continuing their investigation of the 2014 murder of Sheila Von Wiese-Mack by her daughter, Heather Mack.

A search warrant unsealed Friday shows a federal magistrate judge in January signed off on a warrant to search data on an iPhone FBI investigators believe belonged to Heather Mack. It is hoped data from the phone might point them to others who helped Mack and her boyfriend, Tommy Schaefer, plot the murder. Mack and Schaefer both have been convicted in Indonesia for killing Von Wiese Mack at a Bali resort then stuffing the 62-year-old’s body into a suitcase.

Based on text messages recovered from Schaefer’s phone, federal prosecutors in Chicago in 2015 charged Schaefer’s cousin, Robert “Ryan” Bibbs, with helping plot the murder. The warrant application was filed in connection with Bibbs’ case in January, weeks after Bibbs entered a guilty plea in a deal with prosecutors.

Schaefer and Mack, who are serving prison sentences in Indonesia for the murder, have not been charged with any crime in the U.S., but investigators believe there may be more information about Von Wiese Mack’s murder on an iPhone recovered by Indonesian authorities that apparently has never been unlocked by investigators.

Indonesian officials in the fall of 2016 gave the FBI two iPhones recovered when Schaefer and Mack were arrested, though only Schaefer’s phone was unlocked by investigators ahead of their trial in Indonesia, according to the warrant.

Robert Bibbs. | Jon Seidel/Sun-Times

The warrant states the FBI intends to either hack the iPhone or get information from Apple that will allow them to comb through data on the phone to find text messages, location information and even photos that could lead to other people involved in the murder, noting investigators only learned about Bibbs’ role in the killing from information on Schaefer’s phone.

Text messages on Schaefer’s phone showed Bibbs and Schaefer exchanging texts frequently the night Schaefer bludgeoned Von Wiese Mack to death, with Bibbs providing encouragement and advice.

Bibbs appeared in court Friday for a hearing on his plea deal with prosecutors; at the hearing, Assistant U.S. Attorney Bolling Haxall complained that Bibbs had flunked nine drug tests while free on bond in his case. Bibbs’ attorney, Donna Ann Hickstein Foley, told U.S. District Judge Rebecca Pallmeyer that Bibbs had been smoking marijuana heavily, but had been clean since failing his last drug test on Feb. 2. Pallmeyer said she would wait to rule on Bibbs’ violation of his pre-trial release conditions until after reviewing a report on treatment options for Bibbs.

At his change of plea hearing, Bibbs said he never believed his cousin would actually go through with Von Wiese Mack’s murder, even after months of exchanging messages with the couple in which he suggested various means of killing the Chicago socialite.

Bibbs admitted that he turned down an offer of $50,000 from Mack to kill Von Wiese Mack himself, though he thought he would get a share of Von Wiese Mack’s fortune, which Mack believed was about $11 million. The actual size of Von Wiese Mack’s estate is closer to $1.5 million, prosecutors have said.

Mack, who was pregnant when she committed the murder, gave birth to a daughter while in prison two years ago, and a Cook County judge is weighing whether Mack can inherit her mother’s estate.