BOSTON - A third Boston police officer pleaded guilty Thursday to drug trafficking charges for protecting truckloads of cocaine during an FBI sting operation.

Roberto Pulido, 42, entered the plea following two days of damaging testimony at his federal trial.

Authorities said Pulido was the ringleader of a group of three officers who received thousands of dollars from men they believed were drug dealers, but were actually undercover FBI agents. The officers escorted two truckloads of cocaine into Boston in 2006. They were arrested in July 2006 in Miami, where they went to collect $35,000 for protecting a drug shipment a month earlier.

Prosecutors played recordings of conversations in which Pulido was heard discussing the drug protection, as well as other criminal activities he was allegedly involved in, including the sale of steroids and the buying and selling of fraudulent store gift cards.

Pulido's attorney, Rudolph Miller, did not return a message left Thursday by The Associated Press. He told The Boston Globe that Pulido wanted to spare his family, particularly his elderly mother, from having to endure a trial.

Pulido has been suspended from the Boston Police Department since his arrest.

The other two officers, Nelson Carrasquillo, 36, and Carlos Pizarro, 37, pleaded guilty earlier this year to drug trafficking and conspiracy charges.

Pulido pleaded guilty to three charges: conspiracy to possess with intent to distribute more than five kilograms of cocaine and more than one kilogram of heroin and two counts of attempting to aid and abet the distribution of more than five kilograms of cocaine. He pleaded no contest to a charge of carrying a firearm during a drug trafficking crime.

FBI agent Kevin Constantine testified that the investigation began in 2003 after a childhood friend of Pulido's was arrested in Philadelphia. The friend began providing authorities with information about Pulido's suspected role in the fraudulent gift card operation.

Sentencing was scheduled for Feb. 6.