PROVIDENCE –– The federal CVS corruption trial enters its second week today with the government’s star witness expected to take the stand –– John Celona.

Celona is the imprisoned former Rhode Island senator whom the prosecution charges was bribed by the two defendants, former CVS executives John R. “Jack” Kramer and Carlos Ortiz. The defendants face 23 counts of bribery, conspiracy and mail fraud.

Celona is serving a 2½-year federal prison term after pleading guilty to selling his office to CVS, Blue Cross & Blue Shield of Rhode Island and Roger Williams Medical Center.

When he testified in the trial of former Roger Williams executives, Celona was combative with defense lawyers, which undermined his credibility with jurors.

Still, his testimony, backed by documents including e-mails and other correspondence, helped win convictions of Robert Urciuoli and Frances Driscoll on charges similar to those Kramer and Ortiz are facing.

Another parallel in that case: Roger Williams claimed that it hired Celona as a consultant to promote the hospital and its affiliated assisted-living center, through his television show and among senior citizens. But the prosecution argued that they paid Celona for his political clout at the State House.

(The convictions of Urciuoli and Driscoll were later overturned on appeal for other reasons, involving the judge’s instructions to the jury on one particular charge. A new trial has yet to be scheduled.)

Lawyers did not say whether Celona would be today’s leadoff witness in U.S. District Court or if another CVS employee will testify first. But when he does take the stand, he could be there for several days.

— MIKE STANTON