HARRISBURG, Pa. - They were known as "random source" dog dealers.

They bought their animals by the hundreds from shady individuals known as "bunchers," who collect dogs from auctions, shelters, the street, theft and "free to good home" pet ads.

Then, prosecutors say, the dealers sold the dogs to some of the nation's leading medical institutions.

Floyd and Susan Martin of Shippensburg were part of a federally sanctioned yet controversial method of procuring animals for medical research, known as Class B or "random source" dog dealers.

But on Thursday, the Martins pleaded guilty in federal court here to illegally purchasing hundreds of dogs for resale to research facilities including Johns Hopkins and Columbia universities.

The Martins, who operated Chestnut Grove Kennel, admitted that they received hundreds of thousands of dollars from research facilities for fraudulently obtained dogs between 2005 and 2010.

Under a deal with prosecutors, Floyd Martin pleaded guilty to one count of mail fraud, for which he will serve a year in prison, while Susan Martin pleaded guilty to a count of conspiracy, for which she will be placed on probation.

The Martins also will be required to pay $300,000 in restitution.

The sentence will not be official until U.S. District Judge John E. Jones III reviews a presentence report ahead of a June 26 sentencing hearing. He could determine if a change in the sentencing is needed.

Assistant U.S. Attorney Michelle Olshefski declined to comment after the hearing.

Susan Martin's attorney, Lawrence Rosen, said only that the Martins were pleased that the case was behind them.

"It was very stressful for them," said Rosen as Susan Martin, 56, helped her husband from the courtroom. Floyd Martin, 57, has multiple sclerosis and other conditions, he told the court.

The case shed light on the shadowy world of dog-dealing for biomedical research.

"We're talking about an abuse-ridden system of acquiring animals for research," said Nancy Blaney, senior federal policy adviser for the Animal Welfare Institute, a national advocacy group. " 'Random source' is what it sounds like it is. They can get animals from individuals who respond to 'free to good home' ads or animals being stolen. We know because they have been traced through micro-chipping."

The guilty pleas come nearly a half-century after a Pennsylvania case involving a Dalmatian named Pepper, stolen from her family's yard and sold to a New York research hospital in 1965, first drew attention to the practice.

Before her owners could track her down, Pepper died as the result of a cardiac pacemaker experiment. But her story helped win passage of the federal Animal Welfare Act in 1966, establishing humane standards for animals in laboratory settings and regulating dealers who sold to them.