The associate professor was confronted in San Diego about an alleged child predator incident. San Diego police were called and are investigating.

A UC San Diego professor is being investigated after a video confrontation with a private citizen about an alleged child predator crime.

In the video, posted to Instagram by the account @timjohnson.458, UCSD associate professor of chemical and nano engineering Nisarg Shah is shown at a grocery store in San Diego after allegedly arranging to meet up with whom Shah believed to be a boy, 14.

In the Aug 3 video, labeled “People v. Preds Catch 539,” Shah is recorded being surprised by the videographer, who posed as a teenage boy online. The video then shows portions of a lengthy conversation outside the store with Shah about Shah’s motives.

As recorded in the video, Shah said the confrontation is the “worst that I’ve ever felt … what I did was frankly abhorrent. … I need to maybe get help.”

Towards the end of the video, police officers arrive and tell the videographer they cannot arrest Shah. The video and meeting setup cannot be used as evidence, as the videographer is not a law enforcement officer.

The Instagram account owner declined to comment or share images.

The San Diego Police Department is now investigating Shah, police Lt Travis Easter told lajolla.ca, adding that investigation details cannot be shared.

Shah is not currently under arrest, as SDPD needs to conduct its own, standalone investigation.

“We normally don’t work with vigilantes,” Easter said. ”It can be dangerous for everyone involved. … Best to leave it be.”

Shah did not respond to a request for comment.