Seattle police are tracking down the history of a nonfunctional missile launcher that showed up at a weapons buyback program.

Detective Mark Jamieson says a man standing outside the event on Saturday bought the military weapon for $100 from another person there. The single-use device had already been used. It's a launch tube assembly for a Stinger portable surface-to-air missile.

He says detectives will notify the Army Criminal Investigation Command on Monday.

Jamieson says the launcher is a controlled military item and that's not available to civilians through any surplus or disposal program offered by the government. He says it's most likely that the launch tube was previously obtained unlawfully from the military, and would likely be returned to Joint Base Lewis-McChord.

The gun buyback in a parking lot in downtown Seattle was scheduled to go from 9 a.m. to 3 p.m., but ended early because of the large crowd. Police say that after two hours, more than 160 guns had been turned in and $35,000 in gift cards had been distributed. Other buybacks are planned for later this year.

Seattle Mayor Mike McGinn and other leaders have praised the buyback effort, saying it will reduce gun violence. But statistics show a previous effort in Seattle failed to do that.

In the six months after Seattle's 1992 gun buyback — the city's only other such effort — the average number of firearms-related homicides increased. The mean number of firearms-related assaults in Seattle also increased, as did the mean number of robberies with guns. Even the mean number of accidental shooting deaths more than doubled, according to data in a government journal.

The city has collected donations totaling nearly $120,000 to pay for a series of gun buyback events.

People will receive up to $100 gift cards for hand guns, shotguns and rifles, and up to $200 for assault weapons. Full gift card value will only be given for working weapons.

A number of cities nationwide have been holding gun buyback programs in the wake of the Sandy Hook shooting. The Christian Science Monitor reported last month that the city of Los Angeles, one of several municipalities to hold a gun buyback event since the Dec. 14 mass shooting in Newton, Conn., collected more than 2,000 firearms – a record, police officials reported.

In New Jersey, Mercer County officials say more than 2,500 weapons were turned in Saturday for cash during a two-day gun buyback program in the state's capital.

The Trenton gun buyback surpassed one in Camden in December that netted more than 1,100 weapons. Mercer County residents received $25 to $250 for each firearm depending on type, condition and legality.

About $100,000 was budgeted but because of the huge turnout, the amount spent is expected to be well over double that. Some participants were given vouchers after money ran out Saturday.

In California, nearly 700 guns are off the streets of San Mateo County and in the hands of law enforcement officials after the latest in a series of what authorities across the San Francisco Bay area have been describing as successful gun buyback programs, officials said Sunday.

In a buyback event held Saturday, the final tally shows that 680 guns — including 24 assault weapons — were turned in at the San Mateo Event Center, said Detective Rebecca Rosenblatt, a San Mateo County sheriff's spokeswoman.

In addition to the assault weapons, 371 long guns and 285 handguns were turned over to officials, Rosenblatt said.

In exchange for the guns, officials paid up to $100 in cash for a handgun, shotgun or rifle, and up to $200 for an assault weapon.

"It was such an awesome turnout that by the end of it we had essentially a pile of guns," Rosenblatt said.

"I would say it was a hugely successful event," she said.

The event, sponsored by San Mateo County Sheriff Greg Munks, San Mateo County Supervisor Adrienne Tissier and U.S. Rep. Jackie Speier, paid out more than $63,000 in cash in exchange for the guns, officials said.

"The success of the gun buyback exceeded our expectations," Speier, a Democrat who represents San Mateo and the surrounding area, said in a statement.

"People are moved to get rid of guns they no longer need or want. Every weapon turned in is one less life that might be lost or damaged by a firearm, whether accidentally or intentionally," the statement said.

The buyback was scheduled to start at 10 a.m. Saturday, but with cars already waiting in line for blocks outside the event center, officials opened the gates early.

Officials planned on destroying the guns collected, unless they had been used in a crime of if they were stolen, Rosenblatt said.

"If we determine any of the guns were lost or stolen, we would do our best to get them back to the rightful owners," Rosenblatt said.

The San Mateo County buyback comes after hundreds of guns were turned over for cash in recent buyback offers in Marin County, San Francisco and Oakland.

Earlier this month, a buyback offer in Marin County was so overwhelmed by people selling their firearms that officials ran out of money. After collecting 827 guns, the Marin County district attorney's office doled out $43,000 for the guns and distributed another $40,000 in vouchers.

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In December, about 600 guns were turned during over to authorities during a buyback in San Francisco and Oakland.

(JOHN S. MARSHALL reported from San Francisco)