A team of 50 armed men, dressed in plainclothes and driving unmarked cars, arrived early in the morning on March 16 at the home in Riyadh, Saudi Arabia, where Omar and Sarah Aljabri lived.

They were looking for the two siblings, now 22 and 20, respectively. The men "roused [Omar and Sarah] from their beds in the early morning hours and ‘disappeared’ them," according to a lawsuit.

“It’s now almost five months from their disappearance and there’s not a single sign,” their brother Khalid Aljabri told BuzzFeed News in a phone interview Friday from Canada. “You really come down to the basic question at this point: Are they alive or dead?”

The siblings’ father, Saad Aljabri, filed a lawsuit in DC federal court on Thursday against Crown Prince Mohammed bin Salman (MBS) and other top Saudi officials, alleging that the powerful royal is trying to kill him because of his knowledge about the Saudi regime. Other family members have been kidnapped and tortured to leverage Aljabri’s return to the country, the lawsuit says, including his brother and nephew.

Saad, an ex-official who was ousted from the Saudi government in September 2015, hasn’t seen them since, and the pain is taking a physical toll on his health. "Dr. Saad was and remains tormented by what is happening to his young son and daughter,” reads the lawsuit.

Officials at the Saudi Embassy in Washington, DC, did not immediately respond to a request for comment.

Aljabri had worked in the Saudi government since 1976 and was a longtime adviser to the crown prince's predecessor, Mohammad bin Nayef, until his ouster in June 2017, when MBS assumed the role. Aljabri served as a state minister for King Salman and was integral to the country’s counterterrorism intelligence.

In July 2015, Aljabri met with former CIA director John Brennan and reportedly told him that Crown Prince Mohammed was encouraging Russia’s involvement in the Syrian civil war. The crown prince removed Aljabri from his post that September.

Decades of experience in the Saudi government provided Aljabri with knowledge of the crown prince's "covert political scheming," "corrupt business dealings," and the formation of the hit squad that killed Washington Post columnist Jamal Khashoggi, the legal complaint states. (Western intelligence agencies have said MBS ordered Khasoggi's death, but the crown prince has insisted he had no knowledge).

"Few places hold more sensitive, humiliating, and damning information about [the crown prince] than the mind and memory of Dr. Saad-except perhaps the recordings Dr. Saad made in anticipation of his killing," the lawsuit states.

Saad Aljabri alleges that in 2018, just two weeks after Khashoggi’s death, MBS sent a hit squad, or “tiger squad,” to Canada, where he has been living in exile, to kill him. But they were blocked from entering the country by Canada border agents.

This wasn’t the first time the crown prince had allegedly targeted his children; on the first day Mohammed bin Salman was appointed, on June 21, 2017, he enacted a travel ban that prevented Sarah and Omar (then 17 and 18) from flying from Saudi Arabia to Boston. Border security stopped the siblings. The crown prince ignored Aljabri's WhatsApp messages in which he pleaded to let his children go, the lawsuit says.

“This is how we found out: a FaceTime call from Sarah in the airport, crying,” recalled Khalid. “This is a young girl who’s 17 who was ecstatic when she got her student visa, looking forward to life in Boston, and then security officers at the airport tell them, ‘You can’t travel.’ She was crying, she couldn’t understand.”

According to the #SaveJabris website, which was established to publicize their disappearance, Sarah is an architectural engineering student who was kidnapped a few days after her 20th birthday. Omar is a 22-year-old computer science student at Prince Sultan University in Riyadh, Saudi Arabia, who regularly helped organize events at the school.

Sarah and Omar had been accepted and were paying tuition at the International Baccalaureate Program at the British International School and the Suffolk University, respectively, both in Boston, the complaint says, and both schools had contacted US immigration authorities about their absences.

Three months later, in September, Saad Aljabri asked the crown prince to let his children go. The crown prince allegedly responded that if he didn’t return to the Saudi kingdom, he would be targeted and killed.

Omar’s and Sarah’s whereabouts are still unknown. A tracker on the #SaveJabris site notes that it’s been more than 140 days since the alleged abduction.

“At the center of this story, there’s a couple of innocent people, like, sweethearts - they have nothing to do with any political intrigue or any state secrets or whatever the Saudis are trying to spin,” said Khalid. “They are a couple of children. Sarah should be back in my mother’s arms and Omar should be back with my dad, teasing and arguing with him.”