The driver of a car that may have sideswiped a school bus before it nose-dived off an interstate overpass, killing four students, told investigators his steering system may have malfunctioned, according to an investigator.

Gary Van Etten, the investigator in charge of the probe for the National Transportation Safety Board, said late Monday that the car's driver, also a student at Lee High School, told investigators "he was having problems steering the car and they got progressively worse when he lost control of the car."

Witnesses say that car came up on a side lane and apparently hit the bus. Both vehicles were on their way to a technical center where students can receive special science and math credits. Police said the 17-year-old has received death threats since the Nov. 20 crash.

Local officials and the NTSB are investigating the crash.

Earlier Monday, parents, teachers and students, some on crutches, limping or with cuts and bruises, attended the funeral for a 17-year-old girl who was among four students killed.

Thousands went to the funerals of Crystalle Renee McCrary's schoolmates during the holiday weekend as people in the school and community struggled to deal with the fatal crash.

Nicole Sharika Ford, 19, was buried Friday. Tanesha Estella Hill, 17, and Christine Collier, 16, were laid to rest Saturday.

Two of the girls died at the scene, and two others died later. Forty Lee High School students were aboard the bus when it plunged about 30 feet and crashed onto a street.

Huntsville schools observed a moment of silence at 10:10 a.m., the moment of the crash.

At Lee High School, principal Brenda Chunn read the girls' names and rang a bell after each, city schools spokesman Keith Ward said.

"There were a few tears, but it was a very solemn, very somber moment," he said.

Ward said officials will spend this week trying to get back into a normal routine while still acknowledging students' grief.

The tech classes will resume Tuesday, Ward said. Students now will be bused to the center using a route that doesn't include taking I-565, but will still be allowed to drive their own cars to the center, he said.

Anthony Scott, the bus driver, remained hospitalized Monday, along with two student passengers, hospital officials said.

A nonprofit charitable organization delivered 900 teddy bears to students Monday.

"After they were passed out ... every student was carrying around a teddy bear," Ward said. "It sounds like a very simple gesture, but sometimes the simple gestures mean a lot."