According to police, a passenger complained about the camera being placed in the bathroom

Local News
BOSTON (AP) — Massachusetts state police escorted a flight attendant on an American Airlines passenger jet after receiving a complaint about a camera allegedly installed in a bathroom on board the plane.
Passengers aboard American Airlines Flight 1441, which was flying from Charlotte to Boston, told local media that a woman reported that her teenage daughter noticed the camera in the first class lavatory.
Police officers met the plane at the gate after it landed on September 2nd.
The Massachusetts State Police initially responded WSOC-TV in North Carolina that the incident involved a teenager, a flight attendant and a cell phone. However, the State Police later left the FBI as the primary investigative agency because the incident occurred in the air, where the FBI has jurisdiction. An FBI spokesman said the agency had no comment Friday.
“We take this matter very seriously and are cooperating fully with law enforcement in their investigation as safety is our top priority,” American Airlines said in a statement.