Courtesy Antonio GarciaJairo Pastoressa was deemed “mentally unfit” to stand trial in the Oct. 25 murder of Christopher Jusko.

In the days since Christopher Jusko was killed, his step-sister, Christina Rumpf, has ridden a range of emotions, heightened since Wednesday when she learned that the man who the authorities said fatally stabbed Mr. Jusko has been deemed “mentally unfit” to stand trial.

Now, Ms. Rumpf feels sadness for what she says is essentially the loss of two young lives.

“I’ve always felt that living the rest of your life with the guilt of knowing you killed an innocent person is a certain kind of punishment, one that no court verdict will ever alter,” Ms. Rumpf told The Local. “One man made one quick decision and took two lives: my brother’s and his own. There really is no justice in a situation like this, only sad stories.”

On Wednesday, Jairo Pastoressa, 25 – who the authorities said killed Mr. Jusko Oct. 25 after a dispute over a woman in whom both had a romantic interest – was ordered to undergo treatment at the Kirby Forensic Psychiatric Center on Ward’s Island.

Ms. Rumpf learned of the development from The Local and said that her family continues to cope with the loss of Mr. Jusko, who was 21.

“This has been an extremely hard time for my family,” Ms. Rumpf wrote in an e-mail message. “But we’re all doing our best to deal with the shock of losing someone so young in such an unexpected way.”

Friends of Mr. Pastoressa expressed surprise, too, that he stands accused of killing Mr. Jusko.

One acquaintance, Antonio Garcia, an East Village street artist known as “Chico,” said that he mentored Mr. Pastoressa for years and described him as “a lover not a fighter.”

“He never had a father figure,” Mr. Garcia said in an interview. “I was like his father, and I’d give him advice to do the right thing. That’s why I’m disappointed, I failed.”

Mr. Garcia recalled how Mr. Pastoressa would peer out the window of his old apartment by Tompkins Square Park as a child and watch Mr. Garcia do street art.

“I met him when I was doing a painting, and he approached me and said he’s an artist, too,” said Garcia, but according to him Mr. Pastoressa “wasn’t ready yet.”

Mr. Pastoressa came back two more times over the next few years, and finally Garcia went to look at his art — intricately designed t-shirts and canvases.

Meredith Hoffman A memorial to Mr. Jusko developed on East Seventh Street in the days after he was killed.

“I figured he had talent,” said Mr. Garcia, who began taking Mr. Pastoressa to work on murals throughout the East Village, such as one of President Obama that was formerly on East Sixth Street.

Mr. Garcia, who worked with New York City Housing Authority, helped Mr. Pastoressa get a job there two years ago. For four months, Mr. Pastoressa worked painting murals and backdrops of children’s shows.

Since then, Mr. Garcia said Mr. Pastoressa hasn’t had a job, but rather has been “trying to make music,” and has dated several girls.

“Girls and girls and girls,” Mr. Garcia said. “I said, “Jairo, make up your mind, which one you going to take?”

Claire Glass contributed information to this report.