Attorney General Eric Holder said Thursday he would not rule out expanding an investigation of alleged torture under the Bush administration to include the officials who approved the interrogation techniques and the members of Congress who knew about them. 

Holder was pointedly asked about the terms of such an investigation by Sen. Lamar Alexander, R-Tenn., during a Senate hearing Thursday. 

Alexander, echoing claims by fellow conservatives that Democratic and Republican lawmakers alike knew about the interrogation methods in advance, questioned whether all parties in the loop would be "appropriate" parts of an investigation. 

"If you're going to investigate the lawyers ... I would assume you could also get the people who created the techniques, the officials who approved and the members of Congress who knew about them and may have encouraged them," Alexander said. 

"Hypothetically, that might be true. I don't know," Holder said. 

Though Holder previously has said that intelligence officials who acted in "good faith" and relied on official legal opinions during interrogations will not be prosecuted, he has not defined how wide a net the Justice Department might cast if it pursues a full-fledged probe into the interrogation program. 

His statements Thursday suggested an investigation may not be narrowed to focus only on the lawyers who authored the so-called torture memos. The attorney general added Thursday that he wants to look in a "very concrete way" at an internal ethics report and "see from there whether further action is warranted." 

Holder noted that he is a career prosecutor and hopefully knows how far an investigation needs to go "without needlessly dragging into" an investigation "people that should not be there." 

Conservatives have ridiculed the Obama administration for leaving open the possibility of prosecuting the lawyers who drafted the justification for Bush-era interrogations, and have tried to prove that even critics of the program were on board at the time -- so as to dampen the calls for prosecutions.

The internal ethics review Holder referenced is likely to be submitted in a matter of weeks. However, the review is not expected to recommend criminal prosecution against three Justice Department lawyers who wrote the series of memos justifying the use of enhanced interrogation techniques. 

Liberal groups are still calling for Holder to appoint a special, independent counsel to investigate. 

FOX News' Mike Levine contributed to this report.