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SAN DIEGO – A man who used a stun gun to render his mother defenseless, then fatally stabbed her in the Clairemont home they shared, was sentenced Friday to 26 years to life in prison.

Joseph Robert Burks, 31, was convicted in June of first-degree murder in the July 24, 2017 death of Angela Burks, a longtime, well-loved science teacher at Otay Ranch High School. The victim was stabbed more than 20 times in the head, neck and throat.

Angela Burks’ mother, Josephine Van Atta, said her daughter was looking forward to retirement after 35 years of teaching.

“She worked so hard to get where she was,” Van Atta said. “Joseph put an end to all that.”

Van Atta said Joseph Burks had lived with his mother his whole life and the victim wanted him to move out and get a job.

One of Angela Burks’ former students, Samantha Howard Rogers, wrote a letter to the court, saying that the teacher was responsible for her love of science.

The former student said Angela Burks had the ability to “pour out time and care to others.”

Deputy District Attorney Makenzie Harvey said Angela Burks was in a “desperate” relationship with her son. The victim and her “significant other” male friend had a trip planned for this month after she finished her last year in the classroom, the prosecutor said.

Harvey said the defendant called 911 about 7:15 p.m., telling dispatchers that he had stabbed his mother and that she needed medical attention.

When officers arrived, they found the 58-year-old victim on her back and unresponsive inside the home in the 4300 block of Mount Putnam Avenue. The victim — who had lost a lot of blood — was taken to a trauma center, where she was pronounced dead.

Harvey said the defendant watched his mother die, then cleaned up and made up a story that she attacked him and he had to defend himself.

San Diego police Homicide Detective Christopher Leahy testified that the victim lived on one side of the home and the defendant on the other.

The mother’s side of the home was well maintained and the defendant’s side was messy, with items stacked on top of his bed and an assortment of weapons — including two Samurai swords — lined up against a wall, Leahy said.

There was a mattress in a bathroom and the defendant seemed to be sleeping in there, Leahy said.

Two knives believed used in the attack were found at the scene, and one of them had the blade broken at the handle, according to Leahy.

Superior Court Judge Charles Rogers said the attack was “exceptionally vicious” and that Angela Burks died a “violent death.”

According to evidence at trial, the defendant had purchased a stun gun the day before the murder, the judge said.