A 14-year-old autistic boy who wandered away from his New York school and apparently drowned was marked as being in class by three school employees even though surveillance video shows him getting off the school bus and walking away from campus, authorities said Tuesday.

Half an hour later, when Trevyan Rowe apparently wandered onto a highway bridge over the Genesee River in Rochester, generating multiple 911 calls from alarmed motorists, dispatchers failed to follow protocol and send water rescue crews, city officials said.

The boy's body was pulled from the river on Sunday, after a three-day search involving hundreds of volunteers.

"Had it not been for adult failures, Trevyan Rowe may still be with us," Mayor Lovely Warren said Tuesday at one of two news conferences at which city officials accepted blame for his death.

Several school and 911 center employees have been suspended pending an investigation.

Because Trevyan was not marked absent at the beginning of the school day March 8, his mother did not receive an automated notification and only realized he was missing when he failed to return home hours later. She reported him missing about 5 p.m., more than 10 hours after he was dropped off at School 12.

Reading that 3 teachers marked Trevyon present at 3 different times that day, Only the SpEd teacher marked him absent. The school admits they (mistakenly) did not have him classified as a student w #autism, but a student with a "learning disability" 💔https://t.co/J2j32VqNVc — Laurie M. (@LaurieMit) March 14, 2018

A teacher tried to alter the attendance record when it became known that Trevyan was missing, Rochester School Board President Van White said. The boy's special education teacher correctly marked him as absent, White said.

"We are here for one reason, and that is to take full and complete responsibility for this young man's passing," White told reporters.

Superintendent Barbara Deane-Williams said five school staff members were assigned to usher students from their buses into the school the morning of March 8 but no one noticed when Trevyan got off the bus around 7:30 a.m. and walked in the opposite direction.

Deane-Williams said the boy's school plan classified him as having a learning disability but not autism. She said it also didn't indicate he had a tendency to wander, so he received no special attention or escort upon exiting the school bus.

"It is apparent that we were not as careful as we should have been and there were dire consequences for that," the superintendent said.

She said the district is reviewing why Trevyan wasn't classified in the system as autistic.

At a separate news conference, Warren and emergency officials announced the suspension of six employees of the Monroe County 911 center.

Warren said dispatchers did not follow procedure when they failed to contact the fire department and its dive team after several reports of a person walking on an Interstate 490 bridge over the Genesee River at about 8 a.m. Some callers said the person was on the wrong side of the guardrail. Police Chief Michael Ciminelli said police now believe the person was Trevyan.

A state trooper who was dispatched reported he saw no one.

- By CAROLYN THOMPSON, Associated Press