MARGATE, Fla. -- A retired South Florida teacher has been arrested after he allegedly had sexually explicit conversations and exposed himself to undercover detectives posing as teenagers in chat rooms.

According to the Broward Sheriff's Office, 59-year-old David Shelby, using the screen name "Gringoman466," contacted a person whom he thought was a teenage girl in a chat room in July. For more than a month, BSO said, Shelby had sexually explicit conversations with the person, who was really an undercover BSO detective. Police said Shelby also exposed himself to the detective in a webcam video.

Shelby talked to two other undercover detectives online pretending to be teenage girls during that time, according to BSO.

Investigators identified Shelby, a retired Miami-Dade County Schools math teacher and then-part-time employee of Coral Gables Senior High School, as the man in the chat rooms.

In September, police searched his house and confiscated two computers, one issued by the Miami-Dade County Public Schools and the other by the School Board of Miami-Dade County, BSO said. Detectives said he had used the school computers for the chats, Local 10's Janine Stanwood reported.

Shelby, who was arrested Tuesday, faces charges of computer child exploitation and lewd and lascivious exhibition. He has been released from custody on $51,000 bond.

BSO said it has not received any reports that Shelby had inappropriate contact with any children.

Shelby no longer works at Coral Gables High School, Stanwood reported. No one at the school was available for comment on Wednesday. No one answered the door at Shelby's Margate home.

A representative of the Miami-Dade County Public Schools said Shelby had been an employee since 1972 and is considered a beloved teacher.

Anyone with information is asked to call Broward Crime Stoppers at 954-493-TIPS (8477).