VALMEYER, Illinois (CNN) -- As his family grieved over his violent outburst, a picture began to emerge Sunday of Russell Weston as a man wracked by mental illness.

"He wasn't a monster like I heard on the news ... just a man with a mental problem," said Ronald Callahan, Weston's brother-in-law.

Weston, 41 of Rimini, Montana, is charged with murder after he allegedly burst into the U.S. Capitol on Friday and opened fire with a .38 caliber revolver. He shot two Capitol police officers and wounded a tourist before being shot by police.

Weston's family says he is a paranoid schizophrenic.

'It's just been building up'

"It's just been building up, getting a little worse ... (since) he was in his early 20s," said his father, Russell Weston Sr., 66. "We've been living on the edge when he's here ever since."

Arbah Jo and Russell Weston Sr.

April Weston Callahan, his sister, tearfully apologized to the families of the slain police officers.

"We just didn't know he would ever do anything like this," she said.

His family last saw him after he left the family home in Valmeyer, Illinois. He had shot a dozen or more cats with a shotgun after his grandmother had asked him to do something about the cats on family property.

His father told his son that he had 10 days to find another place to live. He now wishes he could take those words back.

"I wished I never said what I did either," the senior Weston said, breaking into tears. "Wishing, wishing, wishing, and the one wish I have isn't true."

Weston split his time between his cabin in Rimini, Montana, and his family's home in Illinois. He had difficulties with law enforcement authorities in both areas.

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"He had delusions that someone was attempting to get him because he had top-secret knowledge of some kind," said Sheriff Daniel Kelley of Monroe County, Illinois.

Weston visited Washington before

In Montana, Sheriff Tim Campbell said Weston never forgave him after Campbell refused to press charges against an 84-year-old woman who Weston said had hit him.

Weston's cabin in Montana

"He became insultive toward me, and just before I walked away from him, he said, 'You'd better watch your back,'" Campbell said.

Weston complained in letters to the newspaper about him, tried to sue him and talked about him on radio talk shows, Campbell said.

In 1991, Weston wrote two threatening letters to then-Montana Gov. Stan Stephens. Last year, Weston went into a mental hospital after making threats against a Helena resident.

Weston earlier had been investigated by the Secret Service after acquaintances reported hearing him make threats toward the government and President Clinton, but the agency determined he was not imminently dangerous.

Law enforcement sources also told CNN that Weston had traveled to Washington before. He went to CIA headquarters and allegedly told officials that he was a clone and that President Clinton was a clone as well.