Can mass shootings be stopped?

Accent Signage memorial
The remains of a memorial Monday, Oct. 22, 2012, for those killed in a workplace shooting at Accent Signage in Minneapolis. MPR Photo/Jennifer Simonson

Monday's violence marked the sixth or seventeenth, depending on how you tally the data, mass shooting since the violence at Accent Signage in Minneapolis where a man shot six people before killing himself last September.

Details about Monday's killing spree continue to emerge.

"As the investigation into Monday's mass shooting at the Washington Navy Yard progresses, authorities are learning more about the mental state of the gunman, 34-year-old Aaron Alexis. A recent police report indicates Alexis was hearing voices coming from walls," reports NPR's Brian Naylor.

"A 34-year-old civilian contractor and ex-Navy reservist killed 12 people at the Washington Navy Yard, questions are being asked about how a man with a troubled service record and signs of mental instability had clearance to be on base," writes NPR's Scott Neuman.

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"Aaron Alexis, the suspected lone gunman who was killed by police in Monday's attack, was issued a 'secret' level government clearance in March 2008, some three years before being discharged from the Navy, NPR's Tom Bowman said, citing Pentagon officials."

A secret clearance is normally good for 10 years, according to the website

At the time of the shooting, Alexis was working for Hewlett-Packard subcontractor The Experts on a Navy-Marine Corps computer project at the Navy Yard. In a statement sent to NPR, The Experts confirmed that Alexis had been employed "for approximately six months over the last year."

The Experts said its latest background check for Alexis "revealed no issues other than one minor traffic violation." However, at least three arrests have come to light since 2004, as well as an incident last month in which Alexis said he was hearing voices.

Today's Question: Can mass shootings be stopped?