ROCHESTER, N.Y. - James Thompson Jr. first bought the AR-15 semiautomatic rifle in 2005 for target shooting and hunting.

Two years later, the rifle was used when a gang member unleashed its firepower into a Rochester, N.Y., house party, killing a 15-year-old girl.

On that night in June 2007, Carmella Rodgers had slipped out of her house to go to the party. That teenage peccadillo would lead to her death, as she was gunned down by the staccato shots from the AR-15.

In the current conversation and controversy over the AR-15 - the same type of weapon as the Bushmaster .223-caliber rifle used by the gunmen in Webster, N.Y., and Newtown, Conn. - the death of a 15-year-old Rochester girl has not been a focus.

But the death of Carmella Rodgers is telling.

The rifle's pathway reveals one route - and a common one - for a legally purchased firearm to wind its way into criminal circles.

Though handguns are the more common weapon in violent crime, the AR-15 used in the Carmella Rodgers killing had an allure for the gang members who wielded it. While many responsible gun owners have an AR-15 among their collection - 2.1 million of the guns were produced in the U.S. between 1986 and 2009, according to the National Rifle Association - the sleek appearance and semiautomatic capacity also appeals to a criminal element.

"I think the group was intrigued by the mere look of this high-powered rifle," said Assistant U.S. Attorney Douglas Gregory, who prosecuted the gang involved in the Carmella Rodgers slaying.

Police allege that among the guns used by William Spengler Jr. when he fatally shot two Webster volunteer firefighters on Christmas Eve was an AR-15. A little more than a week earlier, Adam Lanza carried out a massacre at an elementary school in Newtown, Conn., with the same type of firearm.

Authorities allege that a former neighbor of Spengler bought the firearms for him, while Lanza used guns stolen from his mother, whom he also killed.

Gun turns up

In June 2007 the upstairs apartment of a Rohr Street home was jam-packed for a house party. Carmella was among the crowd.

Also among the partiers were several young men embroiled in a feud with a rival gang, which sometimes called itself the Wolfpack and other times the Chain Gang. In the early hours of the party, they'd refused to allow Wolfpack members to enter.

Some members of the Wolfpack went and grabbed the AR-15 rifle they'd kept for their protection and for crimes. They returned to the Rohr Street house and from the street began firing into the upper-level apartment.

Two men were hit and wounded. Carmella was shot in the chest and died there.

Police found 13 bullet casings at the crime scene, but the rifle was long gone - still in the possession of Wolfpack members.

Two years after the killing, a tow truck driver spotted a rifle in the back seat of an illegally parked car. Rochester police seized the gun, and ran a ballistics test that revealed the AR-15 had been used to kill Carmella Rodgers.

The gun made its way into the hands of Wolfpack members when James Thompson Jr. swapped the AR-15 for $100 and an eight-ball -- cocaine packed into one-eighth ounces for sale.

Thompson bought the AR-15 from a Batavia, N.Y., store for $1,300 in 2005.

A hunter and target shooting enthusiast, he added the gun to his collection, which included a shotgun, an AK-47 and a .30-06 rifle.

Thompson was also a cocaine addict and a drunk.

By 2007 he was buying and using crack cocaine on a daily basis. He'd drive into Rochester, visit a popular street-corner drug area, and purchase multiple eight-balls.

Low on cash and behind on child support, Thompson negotiated a transaction in the spring of 2007 with a dealer - Jerrick Densen, a Wolfpack member known as "D."

Several months later, Wolfpack members used the gun when they shot up the Rohr Street party. While who specifically pulled the trigger is unclear, the federal jury in 2011 determined that three Wolfpack members - Michael Jackson, Russell Hampton and Dearick Smith - were responsible for the death.

Thompson, who according to court records is now clean, was devastated when he learned in 2010 how the gun had been used. He pleaded guilty to a weapons-related crime and testified against the Wolfpack members.

The death of a teenager "was not something that James ever considered when he sold the firearm," his attorney, Assistant Federal Public Defender Mark Hosken, wrote in court papers. "Today, that event is something James thinks about every day of his life."

At trial, Thompson wept when asked about the sale of the gun.

Guns are money

On the streets, especially in drug-dealing circles, guns are currency.

According to Scott Heagney, who heads the Rochester office of the Bureau of Alcohol, Tobacco, Firearms and Explosives, many guns enter the pipeline the same way as the AR-15 used to kill Carmella Rodgers: They are exchanged for drugs.

"What's common about it is the original purchaser of record will divert that gun into illegal commerce," Heagney said.

Stolen guns are also commonly used for crime, research shows.

A review of guns seized by the Rochester police showed that about 15 percent had originally been reported as stolen, according to a 2009 report from RIT's Center for Public Safety Initiatives.

"All these things started as legal at some point in time and end up in the illegal gun market and traded around," said John Klofas, a criminal justice professor at the Rochester Institute of Technology.

Once in the hands of criminals, a firearm can bounce around as easily as baseball cards were once traded by youngsters.

"They turn around and sell the guns for either cash or, specifically, drugs," said Assistant U.S. Attorney Bret Puscheck, who has been involved in many federal gun prosecutions.

The semiautomatic weapons have a certain attraction for criminals, some authorities say.

"There's an advantage to having it," Puscheck said. "No. 1, the capability of the gun. No. 2, they look very intimidating. You flash that thing and people know you mean business."

The AR-15 used to kill Carmella Rodgers was a "community gun," one that, Heagney said, is shared by criminals.

Driven by addiction, Thompson apparently did not consider just how his legally purchased semiautomatic rifle would be used when in the hands of drug dealers. Now 36, he is free after a yearlong prison sentence.

"I must live with this thought of an innocent little girl with a chance for a good life gunned down without a chance," Thompson wrote in a letter to U.S. District Court Judge Charles Siragusa before his 2011 sentencing.

"This is because I gave a street thug a gun."

Gary Craig, Rochester (N.Y.) Democrat and Chronicle