Charlie Tan has been sentenced to 20 years behind bars Monday for federal gun charges related to the death of his father, Lian 'Jim' Tan, president of the Canandaigua-based Dynamax Imaging.

ROCHESTER — He did it. Charlie Tan now admits that he shot his father to death inside the family's Pittsford home in 2015.

Tan confessed to the killing of his father, Jim Tan — president of the Canandaigua-based Dynamax Imaging — in a letter sent to the federal judge that sent Charlie Tan to prison on a gun charge.

In the letter, on page seven, Charlie Tan writes "I entered my parents' home through the back door, walked upstairs, turned into my father's office and shot my father three times as he was sitting at his desk. I knew I had killed him."

Tan says a sheriff's deputy came to the house that night, after the shooting. Tan writes he told the deputy everything was fine.

"My heart was racing but I tried to stay calm," he wrote.

Jim Tan was killed in the home in February 2015. Charlie Tan was a free man when his murder case was thrown out after a hung jury.

Last year in federal court in Syracuse, he pleaded guilty to illegally buying the shotgun that was used to kill his father. At the time he still didn't admit he was the one who did it.

Charlie Tan's confession now is an attempt to get a lesser sentence. According to court documents, he's trying to prove that abuse inside his home lead him to what he describes as being "single-mindedly focused on killing my father."

He's also trying to show that his trial lawyers never used that emotional distress as a defense.

The evidence sent to the court includes an email sent by Jim Tan to Charlie Tan on Christmas Eve, less than two months before the murder.

In the email Jim Tan writes "I really want to kill her," meaning Charlie's mother Jean Tan, "from the bottom of my heart."

Bill Gargan was the prosecutor when Charlie Tan was charged with murder. He now runs the domestic violence bureau in the Monroe County District Attorney's office. He says he was aware of the abuse that was going on inside the Tan home.

Asked whether the abuse put Charlie in a state where he felt killing his father was the only option, Gargan responded, "I wish I could tell you the number of people I've encountered professionaly who have been in situations far worse and yet did not take it upon themselves to murder the abuser."

Gargan said Charlie Tan was offered, but rejected, a plea deal in which he would plead guilty to first-degree manslaughter.

The court is going to take Charlie Tan's confession and all the other documents into consideration and then decide whether there will be a hearing. No hearing has been scheduled at this point.

Charlie Tan is serving 20 years in federal prison for illegally buying the shotgun used to kill Jim Tan.