LOS ANGELES -- The doctor who operated on Kanye West's mother said he thinks he knows why she died, but he won't get specific until after the completion of the coroner's investigation.

Dr. Jan Adams said in Tuesday's Los Angeles Times that he believes he knows "exactly what happened" to Donda West. Speaking about similar cases, he said she could have died of a heart attack, pulmonary embolism or accidental overdose of painkillers prescribed after the surgery.

The hip-hop star's mother died in a Los Angeles-area hospital Nov. 10, the day after Adams performed a breast reduction, tummy tuck and liposuction on her.

The coroner said early indications suggest the 58-year-old died from surgical complications.

Meanwhile, Kanye West was in Oklahoma City on Tuesday to attend funeral services for his mother, which was at 1 p.m. Donda West's parents and brother still live in Oklahoma City, where she was buried, reported KOCO-TV.

Her father, Oklahoma City civil rights leader Portwood Williams Sr., described her as a devoted daughter and respected educator.

"We were real close -- very close," said Williams, who often called his youngest child "Big Girl." "She was just No. 1. One in a million. We have four children, and I've never heard them have an argument with each other. She was just a No. 1 person."

A 1967 graduate of Douglass High School, Donda West attended Virginia Union University before receiving her master's degree from Atlanta University and her doctorate from Auburn University in Alabama.

West began her teaching career at Atlanta's Morris Brown College in the early 1970s. A Fulbright scholar, she became the chairwoman of Chicago State University's English Department.

At Sunday night's American Music Awards, there was a mention of the loss of the rapper's mother last week.

Kanye West wasn't there, but Usher said that his heart and his prayers are with West and his family in their time of grief. And he said that he hopes that West can stay strong as he recovers from his loss.