When a Phoenix-Arizona couple is murdered in their own home,

responding officers consider it one of the cruelest crimes they've ever investigated.

Investigators search for the killer or killers of two beloved grandparents

who devoted their lives to helping others in this episode of Last Seen Alive.

I'm your host, Leah, crime analyst by day, and true crime storyteller by night.

And as always, I'm your co-ist, Scott. Barbara and William Singer were last seen alive in late June of 2014.

They were, respectively, 64 and 81 years old at the time, and lived in northern Phoenix, Arizona. They were a couple,

one of those couples who are a perfect match for each other, and they'd been married for well

over 30 years, going on 40. When they'd first met back in the 70s, it had been instant attraction.

By that point, William, then in his 40s, had long since completed his career in the United

States Marine Corps during which he'd served as a captain and helicopter pilot during the

Korean War era. Since moving on from the military, he devoted himself to a different kind of

service as a helicopter pilot who provided life-saving medevac flights. That is such a cool career.

It is cool.

Now, Barbara had also worked in health care as a nurse,

and it was because of her work as a nurse that she and William had met.

It hadn't happened directly, exactly.

Rather, William's sister, Joe, had had a mother-in-law who'd been a patient in a nursing home.

Joe and the rest of the family had really liked Barbara who'd been working there at the time

and had become convinced that she would get along great with her single family member, William.

So they'd introduced the two of them, and they were right.

William and Barbara had been absolutely taken with

...