A Bellevue gun collector once detained as a material witness in the slaying of a federal prosecutor in Seattle is suing the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives.

Albert K. Kwan was not a suspect in the still-unsolved October 2001 shooting of assistant U.S. attorney Thomas Wales, but investigators detained him for three weeks in 2005 because they believed he might have information about the case.

Kwan's complaint, filed May 20 in U.S. District Court, says that in March the ATF denied him a federal firearms license, which allows people to import, manufacture or sell firearms. It says the ATF found that he had "willfully violated" the Gun Control Act, but it does not say how Kwan allegedly did so.

Kwan's lawyer, Joseph Conte, said last week that he does not believe the denial was related to the Wales investigation. Instead, he said, it was partly because of an earlier dispute in which Kwan had declined to allow ATF agents to search his bedroom during a premises check.

"The one has nothing to do with the other," Conte said.

Kwan has an impressive and valuable collection of weapons and hopes to open a museum, he said, though "there would be some buying and selling."

Kwan previously held four federal firearms licenses that allowed him to manufacture and import firearms in Bellevue and to manufacture firearms in Boise, Idaho. The agency declined to renew his licenses in 2003, saying Kwan had not used them as intended and because he was uncooperative during a premises check.

He sued over that decision, but his complaint was dismissed by a federal judge.

Kwan also sued U.S. Customs and Border Protection in 2003 over the seizure of his van at the Canadian border. The van had a hidden compartment that agents believed could have been used for smuggling. Kwan was never charged and said he simply wanted to be able to store items out of sight. But a judge dismissed his complaint in that case as well.

In 2005, agents searched Kwan's home as part of the investigation into Wales' death. They did not believe he was involved in the killing, but they were trying to track down a gun part that may have been used in it. Wales was killed with a Makarov pistol outfitted with a replacement barrel, and sale records indicated that Kwan had purchased two such barrels.

Kwan denied ever owning more than one barrel, which he turned over to the FBI.

During the search, agents found an unregistered short-barreled rifle, and a jury convicted him of illegally possessing the weapon in 2007. However, Kwan won a motion for a new trial and federal prosecutors dropped the case.

The lawsuit was filed on behalf of Kwan and a business partner, Mark Van Scoy. Van Scoy said that he was not aware the complaint had been filed, and that he wanted a federal firearms license to give him something to do in retirement.