STAMFORD -- Laying on the floor of a back office on the lower level of the Stamford railroad station, Mullen's ears shoot up when his human partner, Metropolitan Transportation Authority Officer Kevin Pimpinelli, gives the cue to move.
A few minutes later, local commuters stopped to look at Mullen, a 6-year-old, 85-pound German shepherd who scampered alongside Pimpinelli, wagging his tail and looking up at the 15-year MTA police veteran.
"After five years we have a strong connection professionally, personally and in other ways," Pimpinelli, 37, said about his rapport with Mullen, who is primarily trained for detecting explosives. "He's always had a very good temperament for a police canine and I swear if this guy could work every day, he would."
This week, Pimpinelli visited the Stamford station with Mullen, part of their regular patrol territory, to discuss their recent triumph -- taking first place in the explosive detection contest at the U.S. Police Canine Association's annual trials, held in late May in Pearl, Miss.
The pair is part of the MTA's K-9 Unit, the nation's largest police explosive detection group, including 50 dogs and as many sworn officers handling them.
The unit is responsible for spot checks of trains, platforms, and other Metro-North, Long Island Railroad and Staten Island Mass Transit facilities. It also more urgently responds to reports of unattended bags and packages.
"The dogs are amazing and I really consider them the major barrier between us and terrorism," Lt. John Kerwick, the unit's commander, said.
Since January, the unit's dog and handler teams have cleared some 65 unattended bags and packages onboard trains and at stations in Connecticut, Metro-North spokeswoman Marjorie Anders said.
MTA Police Sgt. Bill Finacune, who is second in command with the K-9 Unit, said the dogs are an indispensable part of the agency's anti-terror efforts, allowing authorities to quickly determine if an explosive has been found.
"It takes a pretty special dog to work in the transit environment, and because it is a transit environment, a lot of the focus is on the safety of the passengers," Finacune said. "If it's a false alarm, these dogs can prevent a bomb squad from being called and get the trains moving again, and if it's an explosive, they can save lives."
Besides working their regular shifts, Pimpinelli said he runs Mullen through daily obedience drills, as well as 16 hours a month of in-service training alongside fellow teams at the MTA's training facility in Stormville, N.Y.
After a successful search, Pimpinelli rewards Mullen's efforts by allowing him to play with a toy.
"He really is a great working dog," Pimpinelli said. "He doesn't get any snacks and he doesn't even beg for food at home. His big reward is the toy."
Lt. John Kerwick, the unit's tactical commander, said all its dogs are trained to detect explosives, but that more than half are trained in another discipline, such as locating missing persons, fleeing suspects or missing evidence.
Kerwick, also a member of Metro-North's earlier K-9 unit, which ran from 1989 to 1996, said police dogs' specialties have changed from traditional patrol and suspect tracking to being trained to detect explosives or missing people.
In recent years, the agency has added some Labrador retrievers and Belgian malinois, a dog similar to, but often smaller than the German shepherd, for training in bomb detection, Kerwick said.
"The dogs are trained to apprehend people in case we need them to, but to be honest, it is always a sort of last-resort measure," he said. "The dogs are better locators than apprehenders, and, just as a policeman doesn't want to use his gun, if you have a program where the dogs are always biting, your program is going to be over.
"That would be a terrible shame because, used correctly, these dogs are an incredible tool."
Kerwick and Finacune said finding a young dog who has the right mix of personality and physical attributes for explosives detection work in a transit environment can take months, and unit leaders reject about 90 percent and sometimes more of the shepherds, labs, and other dogs that are recommended to them.
The lengthy process usually involves dog dealers who scout out German shepherds and Belgian Malinois litters for the proper attributes, Kerwick said.
"Today dogs can cost $6,000 a piece even before the training," he said. "Even before the training, we have decided whether the dog has a high enough play drive to do the job or is social enough to handle an environment with a lot of people."
Margaret Eckman, a commuter who was traveling to Manhattan from Stamford Wednesday, said Mullen's presence was reassuring to her.
"It gives you a sense that the MTA are keeping their eyes open," Eckman said.
Metro-North President Howard Permut said he believes the K-9 unit plays a role in preventing potential attacks in the New York and Connecticut area.
"The K-9 patrols in Grand Central, and at our outlying stations, are both a deterrent and a very reassuring presence for our customers and our employees," Permut said. "They are a vital component of the railroad's security strategy."