During the prosecution's opening remarks, McInerney's mother broke down in tears as the court read aloud the charges facing her son, which include first-degree murder.
The shooting occurred February 2008. McInerney, now 17, is being tried in Chatsworth after the judge in the case ordered a change of venue out of Ventura County.
Prosecutors said McInerney's actions were deliberate and premeditated and that he waited for the perfect opportunity to shoot and kill 15-year-old Larry King.
Also in court, attorneys described King based on teacher accounts, saying he was a very effeminate boy who was openly gay and didn't have many friends.
Lawyers said 10 to 12 days before he was killed, King was donning eye makeup and at times wearing women's boots with 3-inch heels under his school uniform. Prosecutors said he was taunted mercilessly but had started to give a little attitude back to those who teased him, including McInerney.
One day before the shooting, witnesses said they heard King say, "I love you baby" to McInerney in a mocking tone as the two passed each other in the hallway in school.
Witnesses said McInerney was enraged by this.
The next morning, McInerney, then 14, brought his father's fully loaded .22-caliber pistol to school and shot King in the back of the head twice, killing him in first period English class at E.O. Green Junior High School in Oxnard.
At a preliminary hearing in 2010, detectives testified that white supremacist materials were found in McInerney's bedroom and that King's sexuality was an affront to McInerney's ideology and was a likely motive for the crime.
McInerney is being tried as an adult and faces life in prison if convicted.
In an exclusive interview, McInerney's older brother, James Bing, spoke to Eyewitness News Tuesday. He said Brandon was an "A" student who made a terrible mistake.
"My brother isn't the monster that the district attorney's making him out to be. She calls him all these bad names, that he's such an evil kid, but he's really not. This is the first time he's ever been in trouble in his life in any way. He never had a detention," said Bing.
"Two kids are basically losing their lives. I'm sorry for Larry King's family as well. I feel so sorry for them, but at the same time I want to have my brother back," said Bing.
King's family declined interviews outside the courthouse Tuesday.