Former Massachusetts Probation Department head John J. O’Brien used his influence to turn out attendees for a political fund-raiser for then-Treasurer Timothy Cahill in exchange for a job for his wife, a prosecutor said today in opening statements in O’Brien’s corruption trial.

Defense attorneys for O’Brien, who faces five charges of bribery and corruption, insisted that his wife, Laurie, received her job with the Massachusetts Lottery Commission, which is chaired by the treasurer, without her husband’s involvement.

O’Brien is charged in Suffolk Superior Court in connection with a June 23, 2005, fund-raiser. The event, which was attended by many Probation Department employees, occurred while O’Brien’s wife was applying for a lottery job.

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“We’re not alleging that Laurie O’Brien was unqualified for the job,” said Peter Mullin, assistant attorney general, who is prosecuting the case. “We’re alleging that she got the job through her husband’s illegal means.”

Prosecutors accused O’Brien of working with four other state employees to hatch the plan to produce attendees for the fund-raiser in exchange for the job.

They said they would rely heavily on the testimony of two of those men — Edward Ryan and Fran Wall — to prove that the fund-raiser was a coordinated plan.

Defense attorneys said both men are only testifying against O’Brien to avoid charges themselves.

“Not only is Jack O’Brien not guilty if participating in such a conspiracy,” defense attorney Paul Flavin said. “Such a conspiracy didn’t happen.”