BERKELEY -- A 9-year-old Berkeley boy may have already been dead for up to 36 hours before police found him Wednesday morning, police spokeswoman Sgt. Mary Kusmiss said Friday.

Kusmiss said Amir Hassan's mother, 31-year-old Misti Hassan, was charged with murdering him today based on her statements to police and witnesses as well as extensive writings at her apartment that she said "provide very emotional and strong circumstantial evidence" in the case.

Kusmiss said Misti Hassan's 45 pages of writings over the course of three days "talk about planning for their departure together and walking hand in hand together."

She said Hassan "didn't want to leave Amir behind."

However, Kusmiss said it's not clear why Hassan allegedly killed her son and then apparently tried to take her own life.

"We can's definitively answer that question," Kusmiss said. That lies with her (Hassan).

Kusmiss said officers came to the apartment at 3011 Shattuck Ave. in Berkeley where Hassan lived with Amir shortly before 9:30 a.m. Wednesday after a friend of Hassan's who lives in San Jose flagged down an officer there and that officer called Berkeley police.

She said the friend told police that Hassan had just called her and told her, "I have slit my wrists and cut my neck and killed my son with Klonopin."

Kusmiss said Klonopin is an anti-anxiety medication as well as a sleeping aid.

The Web site Drugs.com says Klonopin is used to treat seizures and panic disorder and may cause drowsiness and be habit-forming.

Kusmiss said that when officers entered the apartment they found Amir, who was a fourth-grader at Emerson Elementary School in Berkeley, lying on a bed with his mother.

Amir was in his pajamas and was "cool to the touch" and Hassan was suffering from wounds that appeared to be self-inflicted, Kusmiss said.

Officers think Amir had been dead for 18 to 36 hours, she said.

Kusmiss said there was no sign of trauma on Amir and no sign of forced entry into the apartment, so officers don't think anyone other than Hassan was involved in Amir's death.

She said an autopsy conducted today indicates that Amir didn't die of natural causes or injuries.

The exact cause of Amir's death won't be known until a toxicology report is completed, Kusmiss said.

Hassan suffered "significant injuries" but they aren't life-threatening and she has been treated at Highland Hospital in Oakland since Wednesday, according to Kusmiss.

She said a judge was scheduled to drive to Highland today to arraign her on murder charges in her hospital room.

Once Hassan's health improves, she will be taken to the Alameda County Jail in Dublin, Kusmiss said.

Kusmiss said privacy laws prevent her from talking about Hassan's medical history.

She said that according to friends and acquaintances, Hassan "reached out to the Police Department for support and help her deal with challenges in the past."

But Kusmiss said neighbors and friends told police that Hassan appeared to be a good mother and they didn't notice anything unusual to be concerned about.

Kusmiss said Hassan apparently was unemployed and said she isn't familiar with Hassan's employment history.

She said Amir's father, Chad A. Reed, has been notified about Amir's death.

Kusmiss described Amir as "congenial" and "a child of warmth" who developed an extended family and "a small community of his own."

She said Amir was last seen by people other than his mother last Sunday, when he played lacrosse and went to a friend's birthday party.

Kusmiss said Amir didn't go to school on Monday because it was a holiday and Hassan kept him home on Tuesday.