Five active members of the New York City Police Department were among a dozen people arrested Tuesday morning as part of a gun trafficking investigation.

The U.S. Attorney's office says it comes after a year-long sting operation involving the Federal Bureau of Investigation and NYPD's Internal Affairs Bureau.

The defendants are accused of trafficking three M-16 rifles, one shotgun and 16 handguns — a majority of which had their serial numbers removed or altered.

The officers arrested are William Masso, 47, an 18-year NYPD veteran working out of Brooklyn's 68th Precinct; Eddie Goris, 31, of Queens; Ali Oklu, 35, of Queens; Gary Ortiz, 27, of Brooklyn; and John Mahoney, 26, of Staten Island.

Goris and Mahoney also work for the 68th Precinct, Ortiz works for the 71st Precinct and Oklu works for the Brooklyn's South Task Force.

Another three defendants, Joseph Trischitta, Marco Venezia and Richard Melnik, retired from the 68th Precinct.

A former city sanitation officer, a New Jersey Correction officer and two other men were arrested as well.

The criminal complaint says Masso, seen above, enlisted the other defendants to help smuggle the guns and steal a half-million dollars' worth of cigarettes from a truck in Virginia, as well as transporting stolen slot machines from Atlantic City to New York.

The involved items carry an estimated street value of over $1 million.

"Officer Masso allegedly suggested to the others defendants that they carry their badges so that if they were stopped they could say they were just off-duty cops," said U.S. Attorney Preet Bharara.

Authorities said the weapons transported by the allegedly corrupt police officers never posed a danger to people on the street.

"The guns that he transported had been rendered inoperable. For all he knew, they were fully capable of being fired at a human being," said Police Commissioner Ray Kelly. "Obviously this is very disturbing and disheartening for members of the department and the community. I can well understand that."

In a statement, the assistant director in charge of the FBI's New York office called the crimes "reprehensible," noting, "The public trusts the police not only to enforce the law, but to obey it. These crimes, as alleged in the complaint, do nothing but undermine public trust and confidence in law enforcement.”

Mayor Michael Bloomberg called the allegations against the policemen in a statement "a deplorable betrayal of the public trust."

He went on to say the arrests do not diminish the NYPD's commitment to keep the city safe, adding, "Because of their dedication and hard work, thousands of guns have been taken off the streets, and thousands of lives have been saved."

Bloomberg has led national efforts to crack down on interstate gun trafficking and he co-chairs the national coalition Mayors Against Illegal Guns.

Bail for all the defendants was set at $100,000.

Masso will also get electronic monitoring and can only leave his house under certain circumstances.

If convicted, the officers could spend anywhere from 10 to 25 years in prison.