Correction: An earlier version of this post incorrectly said, based on information from the Prince George’s County State’s Attorney’s office, that the gun control bill under consideration by the Maryland General Assembly would have prevented a University of Maryland graduate student from legally purchasing the firearm that police say he used to shoot two of his roommates, one of them fatally. The post has been updated to reflect this change.

Media members pass the crime scene on 36th Avenue where two University of Maryland students were shot in a murder/suicide, and a third suffered gunshot wounds, early Feb. 12 in College Park, Md. The three lived in this home. (Bonnie Jo Mount/The Washington Post)

A spokesman for Prince George’s County State’s Attorney Angela Alsobrooks said Wednesday that the University of Maryland graduate student who shot two of his roommates, one fatally, before taking his own life had committed himself voluntarily for mental health treatment in 2011.

John Erzen, the spokesman, and Alsobrooks had told The Washington Post previously that Dayvon Green was committed involuntarily by his mother for four days in December 2011 – months before he legally purchased the handgun and semiautomatic rifle that police say they recovered this month at a College Park crime scene.

Erzen said authorities have since learned that Green checked himself into the hospital but was on his mother’s insurance plan — and that caused some records to be unclear.

“If there was a little bit of confusion on our end, I apologize for that,” Erzen said.

The difference is that the gun control bill that advanced late last week in the Maryland Senate and that is up for debate Wednesday night on the Senate floor would not have prevented Green from legally purchasing the firearm that police say he used in the shooting.

Under the original version of Gov. Martin O’Malley’s (D) legislation, the short commitment would not have automatically banned Green from later purchasing a firearm.

Green also would not have been flagged under a modified plan Senate Democrats approved last week.

In that measure, Maryland would adopt a law similar to one passed in Virginia after the 2007 massacre at Virginia Tech. The measure would prohibit anyone involuntarily committed to a public or private mental health facility for any length of time from purchasing a gun.

The bill would keep the existing 30 consecutive day threshold for patients who voluntarily agree to check into a mental health facility. Those who stay for fewer days would be allowed to purchase a firearm any time after leaving the institution.

Sen. Robert A. Zirkin (D-Baltimore County) proposed stripping the 30-day requirement for voluntary admissions and replacing it with another process. His plan would have banned future gun purchases from patients who are admitted to a hospital for an emergency mental-health evaluation on the recommendation of a doctor, and who then agree to go directly from the hospital to a mental health facility.

It was unclear whether such a measure would have impacted Green.

It is possible that another provision of O’Malley’s original bill – requiring a judge at the time of commitment to make a determination about dangerousness – could have led authorities to ban Green from future gun purchases.

Mental health professionals have resisted placing firearm restrictions on mental health patients who voluntarily seek treatment, saying doing so could deter some patients who might need to own firearms for their employment from seeking needed treatment.

Alsobrooks previously said Green was being treated for symptoms of being bipolar or schizophrenic, though prosecutors and detectives were trying to seek records and other information about his specific diagnosis and treatment plan.

On Wednesday, Erzen said police are still probing the more precise details of Green’s diagnosis and treatment.

It was after Green’s commitment in December 2011 that he legally bought two guns, police have said. He purchased the handgun used in the shooting in April from Just Guns outside of Baltimore, and he purchased a .22-caliber UziB rifle from a gun store in Silver Spring on Jan. 18. Both purchases, police have said, were legal.

Sen. Jamie Raskin (D-Montgomery) , who supported Zirkin’s proposed amendment, said he still hopes the legislature goes further.

“It’s clear the combination of firearms and mental illness is combustible and the public is expecting us to deal with it. We should absolutely err on the side of public safety.”