Key Senate Democrats predicted Monday that the internal investigation into the Judiciary Committee’s leaked memos would be turned into a full-blown criminal investigation.

Exiting a 90-minute briefing about the probe with Senate Sergeant-at-Arms Bill Pickle, a quartet of senior Judiciary Democrats declared that what they had heard led them to believe a criminal inquiry, most likely with the Justice Department handling it, should occur.

“Eventually, this has to be looked at as a criminal matter,” said Sen. Patrick Leahy (D-Vt.), the ranking member on Judiciary.

Leahy sat in on the Senators-only briefing with Sens. Edward Kennedy (D-Mass.), Dianne Feinstein (D-Calif.) and Dick Durbin (D-Ill.), all of whom declined to speak of the details of where Pickle stands in his three-month investigation into how GOP staffers took what now appears to be thousands of Democratic files off of their computers.

While their levels of belief in the probability of a criminal investigation varied slightly, each of the Senators raised the issue of an increasing likelihood that the probe would bring about criminal charges.

“I think there’s a possibility of a criminal investigation,” Feinstein said.

Kennedy added that the accessing of memos was “probably criminal.”

Bruce Artim, chief counsel on the committee for Chairman Orrin Hatch (R-Utah), was allowed to attend the briefing, although all Democratic staff were kicked out early on. After Artim was allowed to attend, Leahy’s chief counsel, Bruce Cohen, also attended the briefing.

The swelling controversy has already resulted in the resignation last week of Majority Leader Bill Frist’s (R-Tenn.) top adviser on judicial nominations, Manuel Miranda, who has admitted to reading Democratic memos when he worked on the Judiciary Committee in 2001 and 2002.

Another committee staffer, a legislative assistant, has already admitted playing a lead role in accessing the Democratic memos and left the committee about a month ago.

Miranda’s resignation letter, a version of which was given to Roll Call and media outlets over the weekend and an updated version of which was circulated Monday, fanned the flames of the investigation even further in Democratic circles. He claimed that “perhaps thousands” of Democratic documents were downloaded off a jointly shared server by the majority and minority staffs.

In Monday’s version of the resignation letter, Miranda also said many GOP staff members on the committee were aware of what was happening, but he stopped short of accusing other staffers of accessing and reading the memos.

“Although I never discussed this with any other colleagues, I knew that other Hatch counsels and staff came to know about the glitch and that some had concluded that the access was not unlawful,” he wrote.

Miranda claimed that of the thousands of documents downloaded, he downloaded files himself only a “few times.” The vast majority of the files were downloaded by the other staffer, and of those, Miranda read only a small percentage.

Durbin said he was stunned by Pickle’s presentation, noting that the “extent and duration of this theft far exceeded” what he thought was involved.

Miranda and a battalion of conservative legal activists have maintained that neither he nor the other former GOP staffer did anything illegal or unethical. They have used phrases such as “technological glitch” to describe what they consider to be a Democratic mistake in having a technology system that allowed GOP staff to read the memos.

As Miranda put it in his resignation letter, “I concluded that these unprotected documents were virtually placed on our desks. From a technology point of view, they were at most left in a common area.”

But Democratic activists cite federal laws saying anyone who “intentionally accesses a computer without authorization or exceeds authorized access” faces up to 10 years in prison. The critical issue in a criminal battle would be the definition of what level of access Miranda and other Republicans had.

Kennedy suggested that when Pickle files his official report, expected to be later this month, Leahy and Hatch would sit down with Frist and Minority Leader Tom Daschle (D-S.D.) to determine the next step.

Presumably, if there were enough evidence to warrant a criminal case, the Justice Department would receive the report and take over the probe, but the Democrats said no determination has been made for how to hand off the probe.

“That has to be resolved,” Durbin said.

And the Democratic Senatorial Campaign Committee jumped on the scandal Monday, issuing an e-mail fundraising alert to supporters that likened the issue to a “high-tech Watergate break-in” and compared it to the 2000 elections in Florida.

“Send a signal that these Watergate-style tactics are wrong,” wrote David Rudd, executive director of the DSCC.

Miranda and other conservatives contend that the Judiciary Democrats are the ones in ethical jeopardy, that the memos that have so far been publicized show a collusion of activity that breaks the chamber’s ethics rules.

Miranda filed a complaint with the Ethics Committee on Friday, alleging that other unpublicized memos show that outside interest groups were promising financial support to certain Senate Democrats in the 2002 elections if unnamed judicial nominations were blocked.

Democrats, in addition to their pushing for a criminal investigation of Miranda and any other Hatch staffer involved in the memo probe, are also privately warning that ethics complaints could be filed with the legal bar associations for any Republican staffer who engaged in accessing the memos or knew of the memos.