According to authorities, Furrow used the gun to fire about 70 bullets, hitting three children, a teen and a 69-year-old receptionist.
Government sources say that in addition to the Uzi look-alike, Furrow's arsenal also included a Glock 9mm pistol, two 308 Brazilian assault rifles, one .22 caliber Davis pistol, an Egyptian-manufactured assault rifle and one Bushmaster AR-15, the civilian version of the M-16.
CBS News Correspondent Vince Gonzales spoke with Richard Dyke, the president of the Maine company that makes the Bushmaster.
"I think if the manufacturer sold the gun illegally or built an illegal gun and saw it go into the marketplace, then he damn well is responsible," said Dyke. "We don't do that. We only sell to people who have a federal firearms license."
Furrow used the Glock Pistol to kill postal worker Joseph Santos Ileto. He bought it and the other weapons in 1996 and 1997. ATF agents have traced almost all of the sales.
Of the estimated 230 million guns in the U.S., more than a million are semi-automatic assault weapons, reports CBS News Correspondent Byron Pitts. And federal agents say that may be a conservative number.
Law-abiding citizens own them for target practice, home security or collector items. But street cops call these guns the 'pit bull of choice' for dope dealers, hate groups or anyone in a hurry to do harm.
Sgt. Robert Rambo, Miami Police SWAT, says the guns are easily concealed. "They have a strap around the shoulder, so when they need it they just swing it out. And they got it and you can hold it with one hand."
Easy to conceal, and easy to find. According to the ATF, 30 percent of the guns used in crimes were stolen from a home or business. But the vast majority are purchased legally by a middle man, then handed over to a criminal.
Even gun store owners say they are becoming reluctant to sell these types of weapons.
Gun shop owner Hector Sehwerert said, "This is a Mac 10. Why sell something like this? That's one of the guns I'd love to see legislation passed against Â… there is no need for something like that. Not for hunting. Not for personal protection."
Isn't it his business to sell as many guns as he can? "It's my business," Sehwerert said, "but I also have a family, I have kids."
CBS News has learned that Furrow was himself a licensed federal firearms dealer from 1992 to 1995.
But the former gun dealer should not have had a single weapon. After assaulting a staff member at a Washington psychiatric hospital, a judge issued an order saying Furrow was ineligible to possess a firearm.
Law enforcement had the authorization to search his home and make sure he had no guns, but they never did. One corrections official said "we planneto, we just hadn't got around to it yet."