Ahmad Yaseen Arain, 20, a bookish computer science student, hurriedly left his family's home in Orange on Friday morning to catch a bus for a meeting with an academic counselor. He was last seen by his younger brother, who dropped him off at a Harbor Boulevard bus stop in Anaheim about 8:30 a.m.

After interviewing family members Monday morning, University of California police - who are leading the investigation - left with Arain's personal computer and expect to review surveillance videos and interview drivers from the buses Arain might have ridden. Police filed a missing-person report with national, state and local authorities late Friday after receiving a call from Arain's family. 

Zahida Arain, Ahmad's mother, said she last spoke to her eldest son on his cellphone about 9:30 Friday morning as he was presumably traveling on a Los Angeles MTA bus to downtown Los Angeles, where he planned to transfer to another bus bound for UCLA. 

She said she admonished him for leaving the house without eating breakfast, and he told her he would buy a late breakfast after his meeting at 11:30.

Arain, who rents an apartment near campus during the school year, had returned home for the summer. It was his first time making the bus journey from Anaheim to UCLA, his brother said.

The mother first grew worried Friday when she telephoned Arain a second time about 11 a.m. and found that his phone had been turned off - something that rarely happened. The family became increasingly concerned throughout the day after Arain missed his appointment, did not attend afternoon Muslim prayers at the school, and did not return home that night.

Arain's mother, brother and his college roommate described him as a religious and quiet man who had held the family together since his father's death in 1997. They all said it was out of character for Arain not to let them know his whereabouts.

"He is a responsible person," Zahida Arain said. 

"He does not like to miss prayers and is very family-oriented. It is not like him to leave home without telling us where he is going. He always lets us know where he is."

His brother said there had been no activity on Arain's credit cards since the disappearance.

Arain, who family members said is enrolled at UCLA on a full scholarship and earns good grades, was preparing to start his senior year at the university. 

Born in Pakistan, Arain moved to the United States as an infant and is a U.S. citizen, his mother said. She said he made several trips to his homeland, most recently in 2002. "He enjoys visiting family members," she said, "but he loves it here in America much more."