Authorities reveal this was no moment of rage. A 13-year-old in Miami allegedly planned his cri::me days in advance, inspired by h0rr0r films and vi0::lent fantasies.

Derek Rosa was 13 when he stabbed his 39-year-old mother, Elina Garcia, as she slept in her bed in their Florida apartment on Oct. 12, 2023

A Florida teen accused of stabbing his mother 46 times pleaded guilty to second-degree murder on Friday, Jan. 16.

Derek Rosa, 15, was sentenced to 25 years in prison. In addition, he will spend 20 years on probation, the Miami Herald reported.

“I’m sorry,” Rosa said at his sentencing in Miami-Dade Circuit Court, according to the Herald.

“I think that he is thankful to everyone that supported him and still supports him,” Rosa’s defense attorney Dayliset Rielo tells PEOPLE.

Rielo says Rosa will go to a youthful offender camp until he’s 21. After that, he will complete the remainder of his sentence at the Department of Corrections.

“I don’t think that children belong in the adult system but I think all things considered, it was a strategic deal,” says Rielo.

Rosa was 13 when he stabbed his 39-year-old mother, Elina Garcia, as she slept in her bed in their apartment in Hialeah on Oct. 12, 2023.

Her newborn daughter was sleeping nearby but was unharmed.

According to a motion obtained by PEOPLE, Rosa allegedly took photos of his mother’s corpse after he killed her and took a selfie with his hand covered in blood.

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

He then allegedly sent a friend images of his mother’s corpse in a pool of blood, a gun and his blood-soaked hand.

Prosecutors said the friend initially thought Rosa was joking but when he learned the images were real, the friend “alternated between shock and disbelief,” per the motion.

Rosa was allegedly fascinated with Jason Voorhees, the hockey-masked killer from the Friday the 13th horror franchise, and told friends he planned to dress as Jason for Halloween, according to WTVJ, citing the motion.

After he killed his mother, Rosa called 911 and allegedly confessing to an operator.

“With today’s guilty plea Derek Rosa admitted what he had previously told a 911 operator and what he had confessed to police detectives, that he murdered his mother,” Miami-Dade State Attorney Katherine Fernandez Rundle said in a statement. “The pain Elina Garcia suffered from the 46 stab wounds could only have been surpassed by the knowledge that the person killing her was her own son.”

When Rosa “stole” his mother’s life, “he also stole so much of his own future,” she said.

During Friday’s sentencing, Rosa’s stepfather Frank Ramos told Rosa he was “like a son.”

“We were a very close-knit family,” he said, per the Herald. “Your mom was a loving mother… Her death destroyed our family and changed our lives forever.”