One of the youngest defendants to ever be charged with homicide in Erie County, will now spend up to 20 years in prison for killing his grandmother.

After pleading guilty by mental illness to third-degree murder in January, today, 16-year-old Hunter Reeser was sentenced 10 to 20 years in prison for killing his grandmother.

"It's been over two and a half years now since Hunter was charged,” said Reeser’s lawyer James Pitonyak.  “I've been doing this for 39 years.  This is probably the most difficult homicide I've ever worked on."

In August of 2016, Reeser was 14-year-old when he shot and killed 60-year-old Sandra Orton, outside of the family's home in Harborcreek.

According to prosecutors, Reeser told police he shot his grandmother in the head as she sat in her van, waiting to take him to a school meeting he didn't want to attend.

"Obviously, the whole situation is a massive tragedy,” said Erie County Assistant District Attorney Paul Sellers.  “It's a family that's been broken and shattered from just every aspect."

The defense tried unsuccessfully to have the case moved to the more lenient juvenile court system, stating Reeser's long history of mental illness, dating back to when he was a young child.

"We had over 2,000 pages of records we had to review,” said Pitonyak.  “He has had signs of mental illness since he was one year and a half of age."

Before sentencing Reeser, Judge Joe Walsh read a letter written by Bob Orton, the victim's husband, and Reeser's step-grandfather.

"Sandy was 15 years younger than me,” Orton wrote.  “I was supposed to go first."

"I don't understand how it happened or why,” Orton wrote.  "I loved Hunter and so did his grandma."

Sellers says the sentence will help Reeser get the treatment that he needs.

"We're hopeful this is an outcome that accounts for the concerns of the community, the safety of the community, and also gets Mr. Reeser on whatever track he needs to be on."

Reeser will be sent to Pine Grove State Correctional Institution, which specializes in youth offenders.

According to Pitonyak, when Reeser is 21, he will be transferred to an adult prison and is eligible for parole when he is 24.