Who was Jack the Ripper? That's a question hundreds of investigators, historians, and authors have sought to answer. Now one man, after 20 years of research and investigation--including grave exhumations and DNA tests--has decided he knows exactly who Jack the Ripper really was.

His own great-great-grandfather.

Starting tonight at 10 p.m. on History, the eight-part limited series American Ripper follows Jeff Mudgett as he lays out his proof.

But the story goes deeper than Mudgett's belief that he is the great-great-grandson of Jack the Ripper--he already knows, beyond doubt, that he is the descendant of one of the first documented serial killers.

"When I was 40 years old," Mudgett says, "at a family dinner party my grandfather revealed a horrible secret. My grandmother had been doing work on our family lineage and my grandfather said, 'You should let sleeping dogs lie' and then he told us about his grandfather, H.H. Holmes. He had kept it from my grandmother; had she known, she probably wouldn't have married him."

Probably not. Herman Webster Mudgett was a doctor from New Hampshire who, after abandoning his first wife and child, changed his name to H.H. Holmes in homage to the fictional detective. He landed in the Chicago area after running from accusations of poisoning, murder, and fraud. He started working at a drugstore, swindled the owners, bought a lot across the street, and built a three-story building that included a drugstore and apartments--plus other "amenities" like airtight rooms, trap doors, and a basement filled with acid vats, quicklime pits, and a crematorium.

Later the building became known as the Murder Castle, where Holmes targeted women who had come to Chicago looking for work. (For the full story, check out Erik Larson's excellent The Devil in the White City.)

"Holmes paid for college by robbing graves and selling the skeletons," Mudgett says. "He was making $2,000 a skeleton--in the 1880s."

So how did Holmes go from con man and grave robber...to killer? "I believe Holmes saw grave robbing as lucrative," Mudgett says, "but realized that putting together a team to rob graves at 1 in the morning was too difficult and time-consuming. So he decided to cut out a step and, instead of robbing graves, kill people to get their skeletons."

As Mudgett says, "The late 1800s was the perfect time to be a serial killer. Law enforcement was overwhelmed; thousands of people went missing, some by choice, some not, every year. So Holmes built a hotel two miles from the World's Fair. He knew thousands of people would flock to the city."

That much is beyond speculation, but still: Holmes was Jack the Ripper? After years of work, Mudgett amassed enough evidence to give a well-received TED Talk on the subject. Then History got involved, Mudgett and the team conducted extensive additional research...and a year later, the series is set to air.

But for Mudgett, the journey has been about more than proving his ancestor was Jack the Ripper.

"So many things came up during this process," Mudgett says. "The human need to determine origin, identify, heritage, and even faith...thoughts about life and death, and whether we should let the dead rest in peace...all those thoughts came up, and they changed the way I thought about a number of very consequential things I had taken for granted. When we were exhuming the body, there were all the scientists and anthropologists there, helicopters were circling overhead, and it struck me right between the eyes: This isn't some Indiana Jones quest. These were real people. The victims were real people. They deserve more than we've given them, and their families deserve to know the truth, even all these years later."

Still, I had to ask: Are H.H. Holmes and Jack the Ripper the same man?

"I absolutely believe H.H. Holmes was Jack the Ripper," Mudgett says. "The fact that the man could have committed those murders is obvious to me, and our evidence--mine, and what the team at History and I uncovered over the last year--will detail that to the audience.