(CNN) A Utah mother is suing a former bus driver who she alleges closed the bus door on her 14-year-old biracial son's backpack and dragged him approximately 150 feet because of his "racial animus" toward students of mixed race.

Brenda Mayes' civil rights lawsuit says her son was getting off the school bus in early February when the driver, John Naisbitt, closed the doors, trapping the boy's backpack inside as he dangled outside.

Naisbitt, 78, then drove approximately 150 to 175 feet before opening the doors and letting the boy go, the lawsuit says.

Naisbitt -- who is no longer employed by the district, per a spokeswoman -- had previously displayed "racial animus and discriminatory conduct" toward other students of mixed race, according to the lawsuit, which cites at least two prior incidents involving other students dating back to September 2017.

Reached by CNN affiliate KSTU at his home in Hooper, Utah, Naisbitt said he was "not at all" racist.

"No," he said. "Look at my dog. He's as black as could be."

Naisbitt told KSTU he retired several days after the incident.

CNN's calls to Naisbitt were not returned.

The lawsuit also names the Davis School District and its transportation director, Dave Roberts, who Mayes said ignored her concerns. The suit requests that disciplinary action be taken against Naisbitt and that criminal charges be filed.

Davis School District spokeswoman Shauna Lund told CNN in a statement Friday morning, "When issues of discrimination are raised at any time, they are investigated thoroughly. The Davis School District takes any claims of racial discrimination seriously and does not tolerate any form of racial discrimination in our schools."

Lawsuit details multiple instances of alleged discrimination

The incident involving Mayes' son -- identified in the lawsuit only as Child Doe -- was caught on the bus camera.

About a dozen students exit the bus before Child Doe steps off.

As he does so, the doors of the bus close on his backpack, and the bus moves forward and continues to do so for approximately 17 seconds. The lawsuit says the bus was moving between 7 and 10 miles per hour. There are several students still in line behind Child Doe, per the video and the lawsuit.

The bus comes to a stop and the doors open, freeing the boy.

"Had the straps on child Does' backpack broken," the lawsuit says, "Doe would have dropped to the pavement and could have been run over and killed by the bus or could have sustained serious injuries by the fall onto the concrete."

Speaking to KSTU, Naisbitt denied that he intentionally closed the doors and claimed the boy staged the incident after Naisbitt disciplined his brother.

"I didn't see him in there," Naisbitt said. "If I had, I would have stopped."

According to the lawsuit, there were at least two other instances of what it called discriminatory conduct against mixed-race students.

In September 2017, the suit says, "Naisbitt took no action when a Caucasian sixth grade boy physically assaulted a third grade biracial girl on the bus." Mayes' son had to "stop the assault."

The incident was reported to the transportation department, the lawsuit says, which was overseen by Dave Roberts.

In October 2018, as two mixed-race boys were getting on the bus after school, "Naisbitt intentionally closed the doors" on one of them. After finally releasing the first student, the lawsuit says, Naisbitt again tried to close the doors on the second.

The first student's parents reported the incident to Roberts, the lawsuit says. When the student's father confronted Naisbitt the next morning, the bus driver "denied even knowing" the boy.

After the father again reported the incident to the school's principal and Roberts, Naisbitt turned up in the bus at the father's place of employment and parked outside, in what the lawsuit calls "a clear attempt to retaliate" against the student by "intimidating or harassing" his father.

Asked by CNN whether any action was taken against Naisbitt in regard to the previous incidents outlined in the lawsuit, the Davis School District declined to comment, citing the pending lawsuit.

School district, transportation director didn't take action, lawsuit says

Per the lawsuit, following the incident with her son, Mayes complained about Naisbitt's behavior to school district administrators, Roberts and others, but they "ignored or deflected many complaints about the racially motivated and abusive conduct," allowing Naisbitt "to continue in his job as a bus driver."

"As a result," the lawsuit says, "his abusive and assaultive behavior on mixed race children continued, with the tacit approval" of district administrators, including Roberts.

The lawsuit claims that had the Davis School District intervened after earlier incidents, Mayes' son would not have been dragged by the bus in February.

The lawsuit asks for unspecified damages from the school district, Roberts and Naisbitt.