OLYMPIA — A Senate panel Tuesday approved a subpoena resolution that seeks documents related to the erroneous early release of thousands of prisoners in Washington state.

On a 4-3 party line vote, the Senate Law and Justice Committee moved the resolution that asks the Rules Committee to issue a subpoena for documents from the Department of Corrections and the governor’s office. The documents sought include any emails, reports or data compilations related to a software coding error that led to the early release of up to 3,200 prisoners since 2002 due to miscalculated sentences. At least two deaths have been tied to the early releases.

“I believe the public is entitled to an investigation, an independent one conducted by this body, that will set forth all the facts in the manner that the public can view and weigh the credibility of these statements of those who may be responsible,” said Republican Sen. Steve O’Ban of Tacoma, the vice chairman of the committee. “Regardless of the fact that the governor is conducting his own investigation, this is a co-equal branch of government.”

The Senate Rules Committee is expected to vote on the resolution Tuesday night, and Lt. Gov. Brad Owen is expected to sign the subpoena immediately afterward.

A software fix to the coding error, publicly disclosed by Gov. Jay Inslee on Dec. 22, was implemented this month. But lawmakers and the governor want to know why something wasn’t done sooner by the Department of Corrections. The agency was first alerted to the error — which started in 2002 — in December 2012. But a scheduled fix for the program was repeatedly delayed over the past three years.

Department of Corrections Secretary Dan Pacholke said he didn’t learn of the error until the middle of last month, and the governor says he didn’t learn of the issue until that same time, when corrections’ officials notified his staff.

Inslee’s office has hired two retired federal prosecutors to investigate, and Democratic members of the Senate committee argued that the committee’s actions were premature in light of that ongoing investigation.

“I certainly agree that we have to get to the bottom of this,” said Sen. David Frockt, D-Seattle. “Once the investigation is complete, by the federal prosecutors, that will begin to give us a window into what actually transpired here. I think our legislative oversight power can be best exercised subsequent to the investigation.”

But O’Ban said he was concerned about the transparency and scope of the investigation conducted by the investigators and said that during a private meeting with them he had been told that employees of the Department of Corrections would not be under oath during their interviews and that their interviews would not be recorded.

“If employees should later disagree with what the investigators claimed those employees shared with investigators in private settings beyond the eyes of the public or media, there’s no way that we can determine that one could establish the disagreement and resolve any doubts about whether those employees gave accurate statements or testimony,” he said.

The committee’s chairman, Republican Sen. Mike Padden of Spokane Valley, said while his committee is initially just seeking subpoena power for documents, it may later ask the Rules committee to approve a subpoena to compel testimony from witnesses, if necessary.

In a written statement late Tuesday, Department of Corrections Secretary Dan Pacholke said that the agency “will continue to fully cooperate with both the legislature’s inquiry, and the independent investigation led by two former federal prosecutors on the miscalculation issue.”