A 23-year-old police officer's son on Wednesday became the third of six Philadelphia prison guards charged in an FBI sting to admit he smuggled drugs and other contraband to inmates in city jails.

With tears streaming down his face, Marc Thompson, formerly employed at the House of Correction in Holmesburg, pleaded guilty to one federal count each of attempted extortion and attempted drug distribution.

He told U.S. District Judge Mark A. Kearney that he accepted a $1,500 bribe to sneak a cellphone, a charger, and 100 OxyContin pills to an inmate who unbeknownst to him was working with the FBI. Thompson faces up to 40 years in prison at a sentencing hearing scheduled for March.

His lawyer, Jack McMahon, characterized Thompson's actions as a significant mistake made only seven months after he was hired as one of the city's youngest corrections officers at the age of 21. He lost his job and his $34,400 annual salary after he was caught on an FBI recording accepting the bribe and delivering the contraband in September 2013.

Thompson was charged along with five other corrections officers caught in the sting. There was no indication that the guards coordinated their schemes, authorities have said.

Louis Giorla, Philadelphia's prisons commissioner, has said the probe grew out of an internal investigation into a growing number of seizures from inmates in city jails. Once the FBI was involved, authorities turned to prison informants to engage those officers suspected of smuggling.

Prosecutors allege that the prisoners made arrangements with guards to meet with an outside associate, who would pay the bribe and provide the requested cellphones and pills. In each case, that associate was recording his interactions with the guards for the FBI.

The pills smuggled into the prisons were placebos, authorities have said.

Two other guards - Bryant Fields, 43, who worked at the Philadelphia Detention Center, and George Kindle, 29, employed at the House of Correction - have pleaded guilty. A fourth is expected to change his plea from not guilty to guilty this month, according to court filings.

Trials for the other two charged corrections officers are scheduled for early 2016.