A former ramp agent for Delta Airlines admitted Tuesday that he tried to bring more than $614,000 in illegal drugs into Atlanta from a flight from Mexico City, federal prosecutors said.

Luis Marroquin pleaded guilty in U.S. District Court, Atlanta, to conspiracy to possess with intent to distribute controlled substances, according to a news release from the U.S. Attorney's Office. The 35-year-old Atlanta man was one of four persons implicated in the plot, and the second to plead guilty.

The scheme centered on a suitcase containing methamphetamine and heroin that arrived Jan. 13 on Delta Flight 364 from Mexico City to Hartsfield-Jackson International Airport.

The plan began to unravel when a Delta agent noticed the unclaimed luggage on a baggage carousel, authorities said. Customs and Border Protection agents inspected the bag and found that it contained drugs.

Homeland Security investigators interviewed Carlos R. Springer, 41, of Hampton, who was in charge of ramp employees who had off-loaded baggage from Flight 364. During a search of Springer's cell phone, agents found coded, incriminating text messages about the suitcase between Springer and Marroquin around the time of Flight 364's arrival, prosecutors said.

Also implicated in the scheme was Kelvin Rondon, 27, of Atlanta, who had been recruited by Marroquin to locate the suitcase of drugs from the aircraft, prosecutors said. A former Delta ramp agent, Rondon pleaded guilty July 19 to the same charge as Marroquin's.

A federal grand jury returned indictments against Marroquin, Springer and Rondon in May.

In June, the grand jury returned a superseding indictment also charging Stephanie Baxter, 26, of Atlanta with concealing and harboring Marroquin while he was a fugitive in the case. Baxter was selling off Marroquin's belongings so that he supposedly could flee to his native Guatemala, but Homeland Security agents foiled the plan and arrested Marroquin in Coral Springs, Fla., on May 8, authorities said.

Sentencing hearings for Marroquin and Rondon have not yet been scheduled. They could receive up to life in prison and fines of up to $10 million, prosecutors said.

Their guilty pleas "demonstrate a continued strong commitment by the U.S. Attorney's Office, U.S. Immigration and Customs Enforcement (ICE), our other law enforcement partners, and airline security teams to uncover, arrest, and successfully prosecute those individuals who traffic illegal drugs through our airport," U.S. Attorney Sally Quillian Yates said in the news release.

Springer's and Baxter's cases are pending in federal court.

The case was investigated by Homeland Security Investigations special agents and task force officers with assistance from Delta corporate security. Assistant U.S. Attorney Michael Herskowitz is prosecuting the case.