Defense attorneys for three people charged in a deadly salmonella outbreak sought to deflect blame and poke holes in the government’s case Tuesday as they questioned a co-defendant, who is a key prosecution witness.

The co-defendant, Samuel Lightsey, was a former manager of a Georgia peanut processing plant blamed in the 2008-09 outbreak. He was indicted along with his former boss, Peanut Corporation of America owner Stewart Parnell, and two others. Lightsey pleaded guilty in May after reaching a deal with prosecutors.

The 76-count indictment accuses Parnell and his brother, food broker Michael Parnell, of shipping tainted products to customers and covering up lab tests showing they contained salmonella. It also charges Stewart Parnell and the plant’s quality assurance manager, Mary Wilkerson, with obstructing justice.

Tom Bondurant, an attorney for Stewart Parnell, asked Lightsey about his plea agreement, which recommends that he not serve more than six years in prison. He had been facing decades behind bars.

Bondurant then pointed out that the government’s lawyers could ask the judge for further leniency, including no prison time, if Lightsey’s able to “substantially assist” their efforts.

“So the truth alone is not enough. You need a scalp to make this deal work, don’t you?” Bondurant said.

Bondurant asked Lightsey a series of questions to demonstrate that Stewart Parnell had given him considerable authority over the Georgia plant and relied on him.

“You made decisions every day about how to run the plant, didn’t you?” Bondurant said.

“That’s the job,” Lightsey responded.

Bondurant also had Lightsey review audits predating the salmonella outbreak that showed the plant receiving high marks from inspectors and a box of what he said was nearly 4,000 lab reports, of which about a dozen tested positive for salmonella.