Law enforcement officials have released new details about a drug “super tunnel” linking San Diego to Mexico.

According to Derek Benner, Special Agent in Charge with U.S. Immigration and Customs Enforcement (ICE), the tunnel connected a warehouse off Drucker Lane in Otay Mesa to another warehouse in Tijuana.

Benner said the tunnel stretches a third of a mile and is 35 feet underground. The passageway itself is 4-feet tall and 3-feet wide.

U.S. Attorney Laura Duffy said engineers and architects had to have built the high-tech tunnel, which is equipped with electricity, ventilation and a rail system.

“These cartels have spent years and tens of millions of dollars in vain,” Duffy said.

Agents found more than eight tons of marijuana and 325 pounds of cocaine inside the tunnel, according to ICE. The drugs have an estimated street value of $6.5 million. Officials said this is the first time they’ve seen cocaine attempt to be smuggled through tunnels.

Officials said the tunnel was recently completed, but not yet operational.

“They did not move one gram of narcotics through that tunnel,” said Bill Sherman, Special Agent in Charge with the Drug Enforcement Administration (DEA.)

Benner had this message for the Sinaloa Cartel:

“We are by no means finished here,” Benner said. “Don’t say we didn’t warn you.”

Three people are in custody in connection with the bust. According to a complaint filed Thursday, Jose Arturo Mendoza and Juan Pena-Osuna each face one count of possession with intent to distribute cocaine. Roman Ramos-Romero faces one count of possession with intent to distribute marijuana. They are expected to be arraigned Friday.

Officials hope there will be more arrests higher up the management chain.

ICE, the DEA, Border Patrol, the U.S. Attorney’s Office, San Diego police, Chula Vista police and the National Guard worked together on the operation.

On Wednesday night, Border Patrol agents and vehicles were seen surrounding the entrance of the Otay Mesa warehouse. The shutdown came after weeks of law enforcement surveillance.

Duffy said this is the fifth “super tunnel” discovered in the area in the past three years, including in Nov. 2011 and on Thanksgiving Day 2010.