Matthew Muller is charged in connection with two crimes police say are related. (Alameda Sheriff’s Officer)

A bizarre kidnapping case that police once called a hoax took yet another surprising turn Monday. The FBI issued a warrant for the arrest of a 38-year-old Harvard Law School graduate in connection with the case and a separate alleged home invasion that occurred last month.

In court documents unsealed Monday, the FBI said that there is probable cause to believe that Matthew D. Muller of Orangevale, Calif., kidnapped Denise Huskins from a Vallejo home on March 23.

At the time, her boyfriend Aaron Quinn told police that assailants entered the home in the early morning, drugged them and tied him up, and disappeared with Huskins. She appeared mysteriously days later in her hometown, unharmed after a person or persons claiming to be her kidnapper demanded thousands of dollars in ransom.

Vallejo Police said after Huskins reappeared that the situation was likely a hoax and that there was no evidence that there had even been a kidnapping.

Months later, the FBI’s statement on Muller’s arrest appears to vindicate Huskins’s and Quinn’s story.

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According to law enforcement, Huskins and Quinn were awakened by a bright light around 3 a.m. that day. A male voice ordered them to lie face down on the bed.

The subject or subjects ordered Huskins to tie Quinn’s hands behind his back and tie his legs, then covered Quinn’s eyes with swim goggles that had been covered with tape and placed headphones on his ears.

“The headphones were used to play a prerecorded message that provided instructions, indicated that the break-in was being performed by a professional group on-site to collect financial debts, and threatened that both victims would be hurt by electric shock or by cutting their faces if either of the two victims did not comply,” according to the FBI.

This undated photo released by the Vallejo Police Department shows Denise Huskins. (Vallejo Police Department via AP)

Police were initially suspicious of Quinn’s story because he did not contact authorities until nearly 2 p.m. that day.

According to the FBI, he said he had fallen asleep and woke up later and freed himself.

On March 25, two days later, Huskins was released unharmed.

On Monday, Huskins and Quinn appeared at a news conference with their lawyers, who assailed police for jumping to conclusions in the original case.

“Do your job, go out, find out if there are other guys, get them in custody as soon as possible and make sure that the next time this happens, they think before they talk,” said Dan Russ, an attorney representing Quinn. “We were confident they were telling the truth.”

“These people … they are absolutely, 100 percent, positively, unequivocally, not just not guilty, they are innocent, they are victims,” said Huskins’s attorney Douglas Rappaport.

Huskins was allegedly sexually assaulted during the kidnapping, according to law enforcement. The Washington Post does not normally name victims of sexual assault, but Huskins and her attorneys identified herself at the news conference.

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Muller had been arrested in connection with a home invasion robbery case on June 5 by the Dublin Police Services of the Alameda County Sheriff’s Department.

In that case, according to court documents, an unnamed subject woke a couple in their home by shining a bright light in their faces at about 3:30 a.m. The female victim ran into the bathroom to call 911. After struggling with the male victim and allegedly hitting him in the head with a flashlight, the suspect fled.

A cellphone left at the scene was used to identify Muller as a suspect.

“That made him pretty easy for us to find,” said Herb Walter, spokesman and investigations lieutenant for the Alameda Sheriff’s Department.

He was arrested at his Lake Tahoe home and was charged with home invasion, burglary, assault with a deadly weapon and great bodily injury in that case.

A pair of swim-style goggles with tape covering the eyes were found in a stolen vehicle found near an address where Muller was located by police. Inside the vehicle, detectives found Muller’s driver’s license as well as a long strand of blond hair that was stuck to the duct tape on the goggles. The FBI noted that the victim in the March 23 abduction, Huskins, had long blonde hair.

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According to court documents, in an interview with police, Muller said he had served as a Marine in the 1990s before attending Harvard. Muller told authorities he had been diagnosed with bipolar disorder in 2008 and suffered from psychosis.

Muller had been admitted to the bar in 2011 and disbarred in 2015. His bar license had been suspended in 2013 according to the State Bar of California and court documents unsealed Monday. According to a Harvard University alumni directory Matthew Daniel Muller of Orangeville, Calif., graduated from Pomona College in 2003 and from Harvard Law School in 2006.

Muller’s attorney Tom Johnson said that when his client appears in court, he plans to plead “not guilty.”

“We’ll also explore how his mental illness which has been ongoing and debilitating factors into his defense,” Johnson told The Washington Post in an interview by phone.

According to Johnson, Muller was discharged honorably from the Marines in 1999 and had received a National Defense Service Medal for his service. Johnson said Muller’s bipolar disorder diagnosis has had a “tremendous impact on his life,” in the past five to seven years.

A Huntington Beach police Crime Scene Investigator is shown at the family home of Denise Huskins in Huntington Beach, California on March 25. (Reuters/Bob Riha Jr.)

Muller is being held by the Alameda Sheriff’s Department, where he has been since June 9. He is expected to be transferred into federal custody.

Because of the similarities between the two cases, police say they believe they were committed by the same individual. They asked others who believe they might have been victims of a similar crime to come forward.

In the Huskins case, several e-mails from her alleged abductors had been sent to a San Francisco Chronicle reporter during and after her alleged kidnapping. In the e-mails, someone claiming to be Huskins’s kidnapper claimed that they were a part of an organized crime ring, according to court documents. It is unclear whether authorities are looking for additional suspects.

Walters said the Alameda Sheriff’s Department is not looking for any other suspects in connection with the June 5 crime.

[This post has been updated.]