(CNN) -

The Justice Department is investigating circumstances surrounding the disappearance of IRS emails that Republicans believe could shed light on the possible targeting of conservative and other political groups by the agency.

The investigation into the email disappearance, which the IRS said was due to a crash of former agency official Lois Lerner's hard drive, is part of a wider criminal probe of whether any IRS employees broke the law in unfairly singling out specific political groups for extra scrutiny.

"The investigation includes investigating the circumstances of the lost emails from Ms. Lerner's computer," according to Deputy Attorney General James Cole in testimony submitted to the House Oversight Committee.

The panel will hold a hearing on the matter on Thursday.

But Cole will also say that he can provide no details as to what investigators have learned because the probe is ongoing.

"The IRS investigation was launched by the department without hesitation and immediately after Ms. Lerner publicly acknowledged the potential misconduct," Justice Department spokeswoman Emily Pierce said in a statement emailed to CNN.

"It has been conducted with the utmost integrity ever since, and department officials have regularly characterized the investigation as a top priority," she added.

Lerner, who ran the division that executed the IRS targeting of groups claiming tax-exempt status, resigned last year after the Treasury Department's inspector general found those working under her used "inappropriate" criteria to scrutinize certain groups.

Since then, she has refused to testify at hearings, invoking her constitutional right not to do so.

That decision and the lost emails have frustrated Republicans, but also amplified their rhetoric and invigorated their push to find any documents related to Lerner and her time in government.