ROYAL OAK, Mich. (FOX 2) - Stephen Mason is charged with felony aggravated stalking stretching for almost two decades.
What's even more disturbing, police say he admitted to stalking thousands of other victims.
Mason, 42, is accused of threatening and stalking a Royal Oak woman for nearly 20 years. Now Royal Oak police say they're unsure how many other victims are out there.
"Whatever motivated him is a little bit unclear," said Royal Oak Police Chief Corrigan O'Donohue.
It started in 2001 when a young woman living in Indiana told police that Stephen Mason began harassing her calling her and threatening her.
The young woman told police at the time she did not even know who he was and the caller ID was blocked.
She began receiving very disturbing phone calls from somebody, there was some indication it might have been someone stalking outside her house.
The harassment continuing for years even when the woman moved to Michigan in 2004.
"She was in a state of terror," said O'Donohue.
When the woman changed her phone number and her name, the calls suddenly stopped. But over a decade later in December of 2018, her phone number ringing again from a blocked number.
"If you can imagine this woman who this has been going on for years, they seem to stop and then pickup, she was in a state of terror," said O'Donohue.
Police say when Mason eventually found the woman in December of 2018, he called her more than a dozen times in one day telling her he had been searching for her for years.
The calls included threats that were violent and sexual in nature with Mason threatening her once again.
"Any kind of investigation that across the state line is very difficult," said O'Donohue.
But Royal Oak police conducted a painstaking investigation which led to finding Mason living in the basement of his mother's home in Anderson, Indiana.
Police there, along with Homeland Security, helped Royal Oak police to search the home arresting Mason earlier this month.
"This individual at the time we served the warrant, was in possession of methamphetamines," O'Donohue said.
Mason's mother even thanked police, telling them she was so scared of him she had been sleeping with a Taser and pepper spray.
Mason also told police he hasn't been stalking just one woman.
"The suspect stated he's had thousands of women that he's been stalking and he claims to keep files on all of them on his home computer," O'Donohue said.
Mason has since been charged with aggravated stalking, a five-year felony and given a $100,000 cash bond. Homeland Security has now taken over the case with many more charges likely.