An elderly woman who, along with her husband, was found dead inside their California home a week ago in a suspected murder-suicide, had been defrauded by a scammer or scammers claiming to be actor Tom Selleck, a longtime friend of the couple tells PEOPLE.

On Friday, May 15, just before 12 p.m., deputies from the Thermal Sheriff’s Station were dispatched to a home on Montego Bay Drive in Bermuda Dunes to perform a welfare check, the Riverside County Sheriff’s Office said in a news release. Inside the home, deputies found Karen Whitaker and Donald Whitaker, who were 79 and 80, with traumatic injuries. The husband and wife were pronounced dead at the scene.

A day before their deaths, their friend Joy Miedecke, 81, who has known the couple for many years, says Karen asked some of her friends for money, claiming Selleck’s manager’s wife had died, and that the manager didn’t have any money.

“That was the last straw for Donald,” Miedecke tells PEOPLE. “He was so embarrassed. He could not believe she would ask her friends to participate in this scam.”

The sheriff’s office says evidence suggests the Whitakers’ deaths were the result of a murder-suicide. Authorities have not said who was responsible.

“Homicide investigators are still actively investigating the incident and will complete a thorough investigation before releasing a final disposition,” the sheriff’s office said.

Miedecke says last summer, Karen began communicating with a person or persons impersonating Selleck; the alleged scam worked by gaining Karen’s trust by using information available on her Facebook profile. Miedecke says the individual or individuals first contacted Karen after she posted a message on the social media platform about a friend who had recently passed away.

“Then, the [scammer or scammers] said, ‘We’re going to come out to the desert and have an event, and Karen, you can be first on the list if you just send $80,’ ” Miedecke says.

Karen and Donald Whitaker.

Courtesy of Joy Miedecke

Miedecke says the amount of money requested — each time in the form of a gift card — gradually grew to thousands of dollars, prompting Miedecke and other friends to urge Karen not to send any funds. According to Miedecke, the friends separately warned Karen that she was being scammed — but Karen remained unconvinced. Miedecke says she believes Karen was experiencing early-stage dementia.

“She thought it was really Tom Selleck,” Miedecke tells PEOPLE. “Nobody could stop her.”

Miedecke says she reported the matter to authorities, and that adult protective services workers visited the couple’s home a few months ago and spoke with Karen and Donald. According to Miedecke, that was when Donald first learned about what had happened. She says that after Donald and the couple’s adult children became aware of the situation, they cut off Karen’s access to financial accounts.

“They cut up her credit cards and took her off of their accounts, but she still found ways to get money and send it to the scammer,” Miedecke says. She estimates Karen sent at least $30,000. “We don’t know the final total.”

Miedecke says Donald had difficulty convincing Karen she had been scammed and could not cope with their financial loss. “He had said a couple of times to friends that he didn’t know how to handle this and he couldn’t cope with it,” Miedecke says.

She says Donald also openly discussed taking his own life, but would add that he would never go through with it because he could not leave Karen with access to their money, because he feared she would spend everything and leave their son and daughter with nothing.

A spokesperson for the sheriff’s office tells PEOPLE the agency had taken a report of financial elder 𝓪𝓫𝓾𝓼𝓮 prior to the couple being found dead but declined to comment further, citing the ongoing investigation.

The sheriff’s office said there is no evidence the unknown suspect or suspects who were involved in the financial 𝓪𝓫𝓾𝓼𝓮 are directly involved in the couple’s deaths.

The agency has asked anyone with information related to this investigation to contact Central Homicide Investigator Hood at (951) 955-2777 or Thermal Station Investigator Gutierrez at (760) 863-8990.

Miedecke hopes that by speaking out publicly, she can help prevent others from being scammed.

“The ramifications of someone stealing all of your money when you’re not capable of earning more money in your lifetime — look at what it causes,” she says.

If you are experiencing domestic violence, call the National Domestic Violence Hotline at 1-800-799-7233, or go to thehotline.org. All calls are toll-free and confidential. The hotline is available 24/7 in more than 170 languages.

If you or someone you know is struggling with mental health challenges, emotional distress, 𝓈𝓊𝒷𝓈𝓉𝒶𝓃𝒸𝑒 use problems, or just needs to talk, call or text 988, or chat at 988lifeline.org 24/7.