WASHINGTON (Reuters) – The U.S. Justice Department said on Tuesday that it is considering a possible ban on certain bump stocks, the attachments that make semiautomatic rifles fire faster and were used in the deadliest mass shooting in modern U.S. history in Las Vegas in October.

The Las Vegas gunman’s use of bump stock to allow his weapons to fire like fully automatic machine guns, killing 58 people and wounding hundreds, has led to rare bipartisan agreement in Congress on the need to review whether they should be banned.

“Possessing firearm parts that are used exclusively in converting a weapon into a machine gun is illegal, except for certain limited circumstances,” U.S. Attorney General Jeff Sessions and the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) said in a joint statement. “Today we begin the process of determining whether or not bump stocks are covered by this prohibition.”

Authorities said Las Vegas shooter Stephen Paddock’s ability to fire hundreds of rounds per minute over a 10-minute period from his 32nd-floor hotel suite was a major factor in the high casualty count. Paddock, 64, killed himself before police stormed his hotel suite.

Previously, Democratic U.S. Senator Dianne Feinstein introduced a bill that would outlaw bump stocks, while several Republicans who have typically opposed gun restrictions signaled a willingness to explore the issue.

As part of the ATF’s review into bump stocks, it plans to publish a notice that will eventually appear in the Federal Register seeking public comment.

The legal analysis will revolve around the definition of the term “machinegun” and whether bump stocks fall in that definition.

The acting director of the ATF, Thomas Brandon, is scheduled to testify on Wednesday before the Senate Judiciary Committee, where he is expected to field questions on bump stocks.

In addition, the hearing will also explore issues related to the government’s database used to conduct background checks on gun buyers, after a man who killed 26 people in a Texas church was left out of the database despite his criminal record.

Last month, Sessions ordered the Federal Bureau of Investigation and the ATF to conduct a review of the gun owner background check database, known as the National Instant Criminal Background Check System, or NICS, to ensure criminals are prevented from buying guns.