WASHINGTON/AURORA - A US police federation chief called for tougher checks on gun buyers, almost a week after a shooter used four weapons, including an assault rifle, to kill 12 people at a cinema in Colorado.

Calls to re-examine America’s gun laws have mounted in the aftermath of the massacre in Aurora, near Denver, during a screening of the latest Batman movie, “The Dark Knight Rises,” that saw the gunman open up on the audience.

Hubert Williams, president of the Police Foundation and chairman of the National Law Enforcement Partnership to Prevent Gun Violence, said he was not calling for new laws but called for tightening up existing measures.

“America is reeling after this tragedy, with people rightly wondering why and how this could happen? And what will be done to prevent the next one, and the next one, and the one after that,” he told reporters in Washington. “Law enforcement is united on this position,” Williams said. “We’re asking for existing laws to be enforced for people purchasing weapons.”

It has emerged that the alleged Aurora gunman James Holmes, a 24-year-old graduate student, managed to obtain part of his arsenal legally over the Internet, but controls on online arms sales are said to be lax.

Over an eight-week period, Holmes stocked up on 6,300 rounds of ammunition: 3,000 for his .233 semi-automatic AR-15 rifle, another 3,000 for his two Glock pistols and 300 cartridges for a pump-action shotgun.

The Police Federation is calling for a ban on sales of large-capacity ammunition magazines. Holmes bought a special magazine for his AR-15 military-style assault rifle that allows a shooter to unload up to 50 to 60 rounds per minute. “After looking at what happened in Aurora, Colorado, who could be in favor of these high capacity magazines?” Williams asked.

According to Baltimore police chief James Johnson, the existing laws only cover the approximately 60 percent of guns that are sold by licensed dealers. The rest, he said, are sold without checks, over the Internet or at gun shows. “How can we possibly allow nearly half the firearm transactions in this country to occur on a no-questions-asked basis?” Johnson asked.

In a speech on Wednesday, US President Barack Obama vowed to pursue “common sense” measures to ensure mentally unbalanced people do not get their hands on guns.

A US judge Friday issued a rare order preventing the University of Colorado Denver from releasing records about suspected Aurora cinema shooter James Holmes.

Much speculation surrounding the 24-year-old’s possible motive in gunning down 12 people and wounding 58 more at a screening of Batman movie “The Dark Knight Rises,” has focused on his time studying neuroscience at the school.

 School documents are usually available under the Colorado Open Records Act, but District Court Judge William Silvester cited a provision that bars the public from viewing open records “prohibited by... the order of any court.”  University officials said Holmes was in the process of withdrawing from the graduate program, but had not completed the necessary paperwork.

At the request of Holmes’s attorneys, Silvester also reinforced an earlier order barring officials of the district attorney’s office and law enforcement officials from releasing information about the case before the trial.

Holmes is being held in solitary confinement at Arapahoe County Detention Center. He could face the death penalty if convicted, though Colorado has only executed one person since capital punishment was reinstated in 1976.