The Portland School District is withholding results of its recently concluded investigation into an alleged incident involving former Deering High football coach Matt Riddell.

“I can’t share the findings due to this being a personnel matter,” Superintendent Emmanuel Caulk wrote in an email late Friday, two days after Riddell resigned.

After a swearing-in ceremony for new school board members on Monday, Caulk refused to answer any questions, such as when the investigation ended, who investigated, the nature of the investigation, and whether it ended because there was a finding or because the person under investigation resigned.

“I’ll respond by email,” he told a Portland Press Herald reporter before walking away. Caulk hadn’t emailed by late Monday night.

The exact nature of the alleged incident isn’t clear, since none of the parties involved will describe what happened, what was said or who was present.

The Maine state director of the NAACP characterized the incident, which was brought to the NAACP’s attention by the parent of a Deering football player, as a matter of “grave concern,” and said the investigation by the district was handled “frivolously.”

Caulk said in his email Friday that “we take all allegations seriously and investigate them fully.”

Rachel Talbot Ross, state director of the NAACP and president of the Portland branch, said the parent contacted the NAACP about two weeks ago. Caulk said he got a complaint on Nov. 11 and announced the next day that there would be an investigation.

Talbot Ross did not return several phone calls and an email left over several days.

Last week, she said the NAACP contacted the school administration and was told of the investigation.

“There was some concern by us on the pace of the investigation,” she said. “While things may be resolved tentatively, there should be expectations for the school department to conduct an investigation in a more timely and professional manner.

“The situation was of grave concern, yet I feel the school administration took it frivolously. There are deeper issues such as how it occurred and how to take action to prevent such things from happening,” she said.

Riddell said Monday that the district had not given him the results of its investigation. Riddell was hired to coach as a contract employee last winter, and is not a member of the faculty.

“I don’t have the official findings, no. But I have a good idea of what they are,” said Riddell, who resigned Wednesday on the eve of the school’s annual Thanksgiving Day game against Portland High. On Monday, he said he resigned for personal reasons.

Riddell would not comment on the matter further, saying he plans to consult an attorney to “find out my options.”

Caulk has said that if a person challenges the findings of a district investigation, the matter could go before the school board.

Members of the school board would not discuss the alleged incident Monday, but the board did add an executive session to its Tuesday meeting that includes a discussion of a personnel issue. Caulk would not confirm if the item is related to the district’s investigation of Riddell.