Nathanael Dougall participates in promotion ceremony for Green Valley Fire District employees in Nov. 2017.

A former Green Valley Fire District captain has been arrested on suspicion of distributing child pornography after an undercover detective recorded his actions in a private messaging application, a federal complaint says.

Nathanael Dougall was arrested in November for distributing images and at least one video within an application "frequently used for trading sexually explicit images and videos," according to the court document.

An undercover detective in North Carolina observed an individual under the username "towerclimber90 — which was later linked to Dougall — posting images and videos in two different private messaging groups between Sept. 20 and Oct. 8, the complaint said.

From Sept. 24 to Oct. 10, Dougall is accused of engaging in private messaging with the detective. Court documents say Dougall requested "dirty" pictures of the detective, who was pretending to be a 14-year-old girl.

Dougall "repeatedly turned the topic to sexual conduct," and “he also sent pictures he represented to be of himself, dressed in firefighting gear, to the undercover detective, and told her he was a firefighter," the court document said.

Authorities identified Dougall by subpoenaing the messaging application, Verizon Wireless and CenturyLink, which all returned information linked to Dougall.

On Nov. 8, federal authorities used a search warrant to seize computers and devices in Dougall's possession, matching the items to IP addresses used within the application. His phone also had "numerous images depicting child pornography," the document said.

Authorities confirmed the pictures sent to the undercover detective matched pictures posted publicly on the Green Valley Fire District's website.

Dougall was fired after the organization learned of the arrest. He served 11 years with the district and was promoted to captain in Nov. 2017.

Contact Star reporter Shaq Davis at 573-4218 or sdavis@tucson.com

On Twitter: @ShaqDavis1