PHILADELPHIA — A suburban Philadelphia landlord placed hidden cameras throughout his apartments and secretly videotaped female tenants for years, investigators believe.

Thomas Daley, 45, of Phoenixville hid cameras behind mirrors and in cabinets and ceiling fans, police said. Some of the cameras turned on with the flip of a light switch, investigators said.

Police found cameras in at least three of 16 apartments he owned in Norristown, they said. The hidden cameras and audio equipment were found in the women's bedrooms, bathrooms and living rooms.

"He had such an elaborate system set up that when someone in the apartment would activate a light switch or a ceiling fan, he was able, via the Internet, to retrieve the video images or audio," said Montgomery County District Attorney Risa Ferman.

No cameras were found in apartments currently rented by men, she said.

Daley told police he had been making the secret recordings for about 20 years, Ferman said.

They have seized a cache of videotapes and DVDs.