Desiree McCartney, Nathaniel Ritz

A 17-year-old from Osgood, Indiana, was sentenced this week to 100 years in prison for the deaths of his two siblings.

Nickalas Kedrowitz was found guilty last year of two counts of murder for the deaths of his 2-year-old sister Desiree McCartney and his 11-month-old stepbrother Nathaniel Ritz. Both children died of suffocation in the family’s home.

Desiree died on May 6, 2017 at Cincinnati Children’s Hospital, and Nathaniel died 81 days later on July 21, 2017.

According to court testimony, police began investigating Kedrowitz after his mother told them that he had previously murdered a kitten. Another family member allegedly said that he had a temper like the Incredible Hulk,Fox 59reports.

Kedrowitz, who was 13 at the time of the killings, allegedly confessed to smothering both toddlers, telling investigators he set his siblings “free from this hell.”

But Kedrowitz' mother, Christina McCartney, defended her son, saying that he was trying to save them from an abusive stepfather.

“He witnessed him being mean to the babies,” McCartney told Fox 59. “That he pushed them down on purpose. He would lock them up in the bedroom to try to shut them up. He painted a pretty bad picture. As a mom, that’s hard to swallow that was going on, and I didn’t know.” She also alleged that Kedrowitz' stepfather directed the killings.

Ripley County Sheriff’s Office

Nickalas Kedrowitz

But Kedrowitz is the only person who has been arrested for the murders, and in court on Tuesday, he was sentenced to 50 years for each murder to be served consecutively.

After the sentencing, Ripley County Prosecuting Attorney Ric Hertel pointed out that the killings were calculated — and said that the harsh punishment was justified.

Want to keep up with the latest crime coverage? Sign up forPEOPLE’s free True Crime newsletterfor breaking crime news, ongoing trial coverage and details of intriguing unsolved cases.

Neither of Kedrowitz’s court-appointed defense attorneys returned PEOPLE’s request for comment.

source: people.com