Story highlights A 12-year-old boy is accused of stabbing to death his 8-year-old sister

The boy pleaded not guilty in a juvenile court in Calaveras County, California, an attorney says

"I say he is innocent," the attorney says

Attorney says he'll raise the issue of whether a 12-year-old can be tried for murder

A 12-year-old accused with stabbing to death his 8-year-old sister at their Northern California home pleaded not guilty on Wednesday during an appearance in a Calaveras County juvenile court, his attorney told CNN.

The boy -- who has not been named because of his age -- is charged with second-degree murder in connection with the killing.

"I say he is innocent," the boy's attorney, Mark Reichel, said. "We are going to come back on July 31 to set a date for a trial on that day and we are getting into the issue of whether a 12-year-old can ever be put on trial for murder."

Leila Fowler and her brother were said to be alone on Saturday, April 27, in their family's Valley Springs home when she was found dead. The 12-year-old told police that he'd seen an intruder leaving the home, then found his sister suffering from stab wounds.

The 8-year-old died minutes after arriving at a hospital, authorities said.

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After the incident, police offered a sketchy description of the suspect as a 6-foot-tall white or Hispanic male with a muscular build.

They also interviewed registered sex offenders in the area, ran down leads and searched in attics, storage sheds and more in the rural, mountainous community located about 60 miles southeast of Sacramento.

Authorities also combed the Fowler's home and neighborhood looking for evidence.

Then on May 11, authorities arrested the boy.

The boy's family, according to the attorney, is supporting him. He is "doing OK under tough circumstances," Reichel said.