Two D.C. schools employees were fired after a 4-year-old student with special needs was strapped into his bus seat in a bus terminal for six and a half hours Tuesday.

The child was in good health and not crying when he was discovered at the Southwest bus terminal at 2:05 p.m., six and a half hours after he had been picked up from his home. City employees failed to notice he hadn't left the bus at his school, and the bus returned to the terminal at 8:52 a.m., leaving him strapped into his car seat and sitting in the terminal for more than five hours.

Two employees were fired from the D.C. Office of the State Superintendent of Education over the incident, spokeswoman Ayan Islam said.

Islam said OSSE, which transports about 3,100 special-education students on more than 600 buses, was "troubled" and "is investigating how this apparent breach in protocol occurred."

Superintendent Hosanna Mahaley called the incident "rare and unbelievable and totally unacceptable." The agency is consulting with the attorney general to decide whether criminal charges should be filed against the two employees, one whom had worked for the city for 10 years, the other for five.

The back of each bus is equipped with an alarm that sounds when the bus is powered off, forcing employees to walk through the bus to check for children. But the alarm had been disabled.

The Washington Examiner reported in July that an 8-year-old boy with autism had to wait almost four hours for a bus to take him home from school after OSSE dispatchers failed to send for his bus -- and then forgot to send for his backup bus when his mother complained. The dispatcher was fired.

Tuesday's incident comes on the heels of a celebration for OSSE. On Nov. 8, a district court judge decided the agency's bus fleet was ready to leave federal court supervision after 17 years. The feds had swooped in when they discovered that students were being transported on buses that hadn't been properly inspected or maintained.

Staff writer Alan Blinder contributed reporting.