Cal Ammouri says he’s as shocked as everyone else that his sisters are gone forever.

He is the sole surviving brother of two Arizona women who died under mysterious circumstances at an assisted suicide clinic in Basel, Switzerland, last month.

Ammouri — who lives in a small, fourth-floor walk-up in Manhattan’s Washington Heights neighborhood — said he never visited upscale Cave Creek, a suburb north of Phoenix, where his two accomplished sisters lived together for years before they left home last month, apparently to die.

But Cal, who is 60 and said he works in IT, claimed they would speak on the phone and said he’s baffled over their apparent decision to check into Pegasos, one of the few suicide clinics in the world that will help people kill themselves even if they’re in perfect health.

The women, Lila Ammouri, 54, and Susan Ammouri Frazier, 46, are believed to have paid $11,000 each to end their lives. Unlike other assisted-suicide organizations in Switzerland, such as Dignitas and Exit, Pegasos, which was established in 2019, accepts applications from people who are not terminally ill. 

“I’m totally devastated and don’t have a clue why they did this,” Ammouri told The Post Friday. “They were so secretive, especially with me. Can someone tell me what happened? Do people snap just like that? It could be. You wake up one day and you don’t feel like life is precious.”

Lila, a palliative care doctor, and Susan, a registered nurse, apparently flew from Phoenix to Orlando, Fla., on Feb. 3, and then on to Zurich without notifying family or friends of specifics, a police source in Phoenix told The Post.

The Pegasos clinic is as secretive as Cal Ammouri said his sisters were. The physical address of the clinic is closely guarded. It employs a company called Coll-Control in Basel to receive its mail.

An alarm was first sounded by friends and colleagues of the Ammouri sisters, who both worked for Aetna Health Care, when the women never returned to work. They were supposed to be back from vacation on Feb. 13. A Facebook group was set up to help find them.

One friend, cardiologist David Biglari, told Fox10 in Phoenix on March 17 that he and others worried that foul play was involved.

Biglari said no one had heard from the sisters since an e-mail was sent from a work laptop on Feb. 9. Then, a text message, purportedly from one of the sisters, was received by a colleague the next day. But Biglari said the text contained misspellings and he thinks it may have been sent by someone pretending to be Lila or Susan.

“Some of the text communications they had, we are certain they were not from them,” Biglari said. “They were most likely fabricated with someone else.”

He said that, prior to the trip, he and others saw no indication that anything was bothering either sister.

“They were in a very good position of their lives in terms of careers and what they have reached and accomplished, and there is no reason for them to not be returning on their own volition,” Biglari added.

Finally, after questions raised by the sisters’ colleagues and an Arizona congressman, US consular officials confirmed on March 23 that the sisters had died last month.

The Basel-Landschaft Public Prosecutor’s Office said that the sisters had ended their lives “within the legal framework” of Switzerland

Selinda Staggers, a medical assistant who worked remotely for four years with Lila, said staffers’ “jaws dropped and they all went silent” when a supervisor told them that the doctor had died but not how.

“She was the nicest, sweetest person,” Staggers said. “Always asked me about myself. She was very normal, very kind, very professional.”

Staggers said she saw no indication that Lila was physically sick or depressed and was astonished to learn she’d gone to Switzerland to die.

Biglari told The Post Thursday that he doesn’t know what to think now that he knows the sisters committed suicide.

“We still need answers,” he said.

Cal Ammouri says he wants answers too and is frustrated by his conversations with Swiss consular officials who, he said, have given him very little information.

The Pegasos clinic did not return an e-mail from The Post seeking comment.

The Daily Mail reported last week that Lili Ammouri had put her $1 million home in a intra-family trust on Jan. 25, an arrangement allowing the home to be transferred to family without the conventional legal process of proving they’re heirs to the property.

Ammouri says he is their only blood relative but knows nothing about the property transfer.

He also swears there were no dark family secrets that he or his sisters have been hiding over the years nor was there any abuse in the family. But he admitted that he hadn’t seen his sisters in at least 30 years.

Like Cal Ammouri, his sisters were childless. Lila had never married but Susan was married briefly, then divorced, from a man who was abusive, according to Cal and a friend of the sisters who did not want to be identified publicly.

“I don’t know why she was ever with him,” Ammouri said. “You can’t just marry the first guy who comes along.”

Cal said he and Lila were born in Chicago and that their parents later moved to Lincoln, Neb., where Susan was born. Their father, Andrew, was a microbiologist who got his degree at South Dakota State, Cal said.

At some point Cal’s parents split up, he said. He and Andrew moved to New York where the father worked for a city lab. His sisters and their mother moved to Arizona.

Faye Ammouri died in 2011 at the age of 75 but there were no records immediately available to indicate Andrew’s death. Cal said his father died “sometime in the past five years” but was vague. Andrew had been living at the same address as Cal, who spoke outside his apartment to a Post reporter.

Cal said that Lila had phoned him on Feb. 10 but did not say she was in Switzerland, and that she sounded normal. A Swiss government official, speaking on condition of anonymity to The Post, said the sisters died on Feb. 11.

According to Cal, the call came from Lila’s familiar Arizona number. Earlier this week, however, he told The Independent that he had last spoken to his sisters sometime in early January.

“I begged them to call me every week but they hardly ever did,” Ammouri said. “I had to be very careful how I talked to them. One slip and it was, ‘Oh, boy.’”

Australian and American documentaries about patients who previously traveled to Pegasos to die give a rare glimpse into the interior of the clinic. The rooms have cinderblock walls painted white, as well as what appears to be a rug pinned to the wall. 

The clinic allows pets inside the rooms to comfort the dying and lets the patients select music to accompany their final moments.

When the time comes, patients are instructed on how to kill themselves, choosing between a lethal drink or death through an intravenous drip. A doctor will hook the patient up to the drip, to insure the needle is inserted correctly, but the patient must push a notch to let its contents flow into their bodies themselves.

A third party must be there to confirm and identify the person after death. Pegasos advises patients who do not have a witness to contact another assisted dying organization called Exit for help. It is unclear who served as witness for the Ammouri sisters, but their brother hopes to find out more.

“I’m not going to quit until I learn what happened,” Cal said. He pointed down the apartment stairwell in the direction of the building mailboxes.

“I’m still hoping I get a letter from them with some explanation.”

Additional reporting by Alexandra Williams