ST CHARLES – A St. Charles native who was wanted for the Sunday murder of a man in California has died after he shot himself at his St. Charles home this afternoon.

Officials on the scene say Mark Allen Sypien, 51, of Dublin, California, who is suspected in the murder of John Moore, 76, of Danville, California arrived at his home on Bittersweet Road, where his parents still reside. They barricaded themselves in the basement upon seeing him arrive at the residence, and a short time later, officials say Sypien shot himself.

Police say he was found on the lawn at about 3 p.m. and was transported to Northwestern Medicenie Delnor Hospital in Geneva with life-threatening injuries, where he later died.

Sypien also has lived in Elburn, Cortland, and DeKalb. He graduated from St. Charles High School in 1986.

Sypien dated Moore's daughter in the late 2000s, according to the San Jose Mercury News. The relationship ended in 2014, but Moore continued to be concerned that Sypien would return with a violent vengeance.

"He is a very volatile sociopath that has been undiagnosed at this point," said a woman who had a relationship with Sypien in Elburn from the mid 1990s until the early 2000s. The Chronicle has granted her anonymity because she was a victim of domestic violence and fears for her safety.

​"He's very manipulative, and right now he snapped and killed one person," the local woman said. " He's threatened me personally, my daughter, and other people around this area, and we are all taking this very seriously at this point."

Sypien has a history of legal trouble in DeKalb County, court records show. He spent 120 days in DeKalb County jail in 2016 after he violated an order of protection that a domestic violence victim had secured against him. His history in Kane County included such incidents as battery domestic battery and violating an order of protection, records show.

Elburn police provided extra presence at two Kaneland District 302 elementary schools Wednesday morning regarding a "potential person of interest."

Around 2:25 p.m. Sunday, Sypien allegedly shot Moore, 76, multiple times in a parking lot in the 3400 block of Fostoria Way, Danville, according to the Mercury News.

Danville police said Sypien fled the scene after the shooting, has not been heard from since, and remains a fugitive considered armed and dangerous.

According to the Mercury News, four years before John Moore was killed, he typed up a restraining order request in 2014 predicting that Sypien would harm him or his family.

"[Sypien's] recent history and past criminal record shows he has the capacity to be violent and harm women without remorse," Moore stated in the request. "I believe he has the capacity to be a sociopath."

In a 2016 email to his family, Moore shared concerns that Sypien would return to California after completing his jail sentence in Sycamore, to begin harassing the Moore family again.

"I believe we need to be more vigilant going forward," Moore wrote.

Moore sent the email after he received a series of profanity-laced messages from Sypien, who said he would "get back in touch ... very soon."

"You honestly can't think I was going to let you destroy ever [sic] aspect of my life and get away with it," Sypien wrote, and in another email to Moore added, "John Moore, the time is now."