Baltimore County Police Chief James Johnson called on the Senate Judiciary Committee to “urgently” pass tougher gun restrictions that he said would “address the rising epidemic of gun violence in this nation.”

Johnson, who testified representing the National Law Enforcement Partnership to Prevent Gun Violence, ticked through a medley of statistics illustrating the personal and economic impact of rising gun violence. In 2010, he said, the cost to the nation of gun violence was $57 billion. And he said firearms had become the leading cause of death for police officers killed in the line of duty.

“On behalf of my colleagues across the nation, I’m here today to tell you that we are long overdue in strengthening the nation’s gun laws,” Johnson said.

Johnson said the private sales loophole in existing law allows roughly 40 percent of firearms to be purchased without a background check. Between November, 2011, and November, 2012, Johnson said, 6.6 million gun transactions occurred without a background check.

“It’s like allowing 40 percent of passengers to board a plane without going through security,” Johnson said. “Would we do this?”

Johnson also called on senators to pass a new assault weapons ban. Since the 1994 assault weapons ban expired in 2004, Johnson said, “I’ve seen an explosion of firepower.”