Liliana and Daniella Moreno are seen in this undated photo.
CNN  — 

Nearly a decade after Liliana Moreno and her 8-year-old daughter Daniella disappeared in the Miami area, federal investigators say they have now arrested a man in the case: The girl’s father.

Gustavo Alfonso Castano Restrepo, 55, of Miami was arrested Monday, days after he was indicted in federal court on one count of kidnapping resulting in death in connection with Liliana’s and Daniella’s 2016 disappearance, court documents show.

But much of the case remains shrouded in mystery to the public and Liliana’s family: Although the two-page indictment filed in US District Court in Miami levies one charge against him – accusing him of kidnapping Liliana, then 42 – it alleges the kidnapping led to the deaths of both Liliana and the child. Authorities have released very few details, including why investigators believe they are dead, how the kidnapping happened, what led them to arrest Castano, and whether they know of a motive.

The indictment’s assertion that Liliana and Daniella are dead “is not what we want to see,” Liliana’s brother Eduardo Moreno told CNN this week.

“We as a family … are trying to find out what happened,” he told CNN by phone.

The mother and daughter, who lived in Doral just northwest of Miami, were last reported to have been seen at or near a Home Depot in nearby Hialeah on May 30, 2016, according to the FBI.

Castano is Daniella’s father, though he “was never involved in Daniella’s life,” Eduardo Moreno told CNN.

Liliana and Castano also knew each other through their careers, her brother said. Liliana was an architect, Castano was in construction, and they had worked together often, the Miami Herald reported.

The US attorney’s office for Florida’s southern district announced the charge on Tuesday. Castano remained in custody following a hearing in front of a federal magistrate judge that day, the office said.

The court documents and the office’s news release do not say whether investigators found Liliana or Daniella dead. The indictment alleges Castano kidnapped Liliana, held her “for reward and otherwise,” and used “a cellular telephone, the internet, a motor vehicle, and the Homestead Extension of Florida’s Turnpike” in committing the crime.

“It is further alleged that the commission of the aforesaid kidnapping resulted” in the deaths of both Liliana and Daniella Moreno, the indictment says, without elaborating.

The FBI – one of the agencies investigating the case, according to prosecutors – cannot discuss ongoing probes like this one, said spokesman Jim Marshall, who pointed to court documents and the US attorney’s news release as the available information. The Miami-Dade Police Department, another agency involved in the case, did not respond to CNN’s request for comment.

CNN contacted the US attorney’s office to ask questions about the case, but did not immediately hear back.

An attorney for Castano, Phil Reizenstein, told CNN on Friday that he was just retained in the case and needed time to investigate, prepare and put together a bond proposal. His office intends to ask that a pretrial detention hearing be held Wednesday, he said.

If convicted, Castano would face a mandatory minimum sentence of life in prison, the release from the US attorney’s office said. The maximum sentence would be death, the office said.

The disappearance

Eduardo spoke to his sister by phone less than an hour before she left her house on May 30, 2016, he told CNN. He didn’t say why she left the house, but added that it was Liliana’s intention to stay at home for the majority of the day.

That day also was the birthday of their sister Carolina, who lives in Colombia with much of the rest of the Morenos’ family, he said.

“They always called her (Carolina) for her birthday,” Eduardo said. But Liliana and Daniella didn’t call Carolina that Monday.

That’s when her family started to worry.

Eduardo, who was in Colombia at that time, said that the family received a call from Castano the morning of May 31 asking if they had heard from Liliana. During the call, Castano vacillated on whether he had last seen Liliana on May 30, or days before that, Eduardo said.

Growing concerned about his sister’s whereabouts, Eduardo asked a friend of Liliana’s living in Doral to check his sister’s home to see if she was there, he said.

“We assumed that Liliana’s car was not at her house, because Gustavo told us that he had looked for Liliana’s car and it was not there,” Eduardo said. But Liliana’s friend said her car was parked in the same place it was usually parked and that no one was home.

Eduardo then decided to get the police involved.

At Liliana’s home, police saw her car in the driveway and food on a stove, and they also found her wallet, CNN affiliate WPLG reported.

The FBI’s missing persons poster for the mother and her child says they were “allegedly last seen at or near the Home Depot located at 13895 Okeechobee Road in Hialeah, Florida.” According to WPLG, Castano told police that Liliana had asked that she and her daughter be dropped off on Florida’s Turnpike at Okeechobee Road – an intersection very close to the Home Depot.

“We want to know what happened,” Eduardo Moreno told CNN. “If something happened to my sister Liliana, where is Daniella?”

“In this case, it is more about finding out what happened or at least trying to bring them back,” he said.

CNN’s Amanda Musa contributed to this report.