The second person was interviewed by the FBI before being cleared by it.
"The unidentified subject has been located interviewed and does not appear to be connected with the yesterday's shooting incident at Oak Creek," a FBI spokesman told PTI on Monday.
Even as the investigation is ongoing, the FBI said the shooting was carried out by the lone gunman identified as Wade Michael Page, who was later shot dead by an Oak Creek police officer.
Earlier on Monday at a news conference, the FBI said they were trying to identify a suspicious man who arrived at the scene after the shooting and released a photograph of him, asking for the public's help.
The investigation is still being treated as a possible case of domestic terrorism, the local police said.
On August 5, six persons were killed and three critically injured when a gunman opened fire inside a Gurdwara in Wisconsin.
The gunman who killed six people at a Wisconsin Sikh temple was a US Army veteran, military sources said on Monday, and a monitor of extremists said he had links to hate groups.
A law enforcement source identified the tall, bald, white gunman as Wade Michael Page, 40. The gunman shot dead six people and seriously wounded three, including a police officer, at the Sikh Temple of Wisconsin on Sunday as worshippers prepared for religious services. A police officer shot Page dead.
The "name that is out there is accurate," the source said. Fox News and CNN had previously identified him.
Authorities said they were treating the attack as an act of domestic terrorism. American Sikhs said they have often been singled out for harassment, and occasionally violent attack, since the September 11, 2001, attacks because of their colorful turbans and beards.
US military sources said Page had been discharged from the Army in 1998 for "patterns of misconduct" and had been cited for being drunk on duty.
Page had served in the military for six years but was never posted overseas. He was a psychological operations specialist and missile repairman who was last stationed at Fort Bragg, North Carolina, the sources said.
In June 1998 he was disciplined for being drunk on duty and had his rank reduced to specialist from sergeant. He was not eligible to re-enlist.
Page had been a member of the racist skinhead band End Apathy, based in Fayetteville, North Carolina, in 2010, said Heidi Beirich, director of the intelligence project at the Southern Poverty Law Center in Montgomery, Alabama.
Page also tried to buy goods from the National Alliance, a neo-Nazi group, in 2000, she said. The SPLC describes the National Alliance on its website as "perhaps the most dangerous and best organized neo-Nazi formation in America."
In a 2010 online interview with End Apathy's record label Label56, Page said he had founded the band in 2005 because "I realized ... that if we could figure out how to end people's apathetic ways it would be the start towards moving forward."
Police were searching an apartment at a duplex in the Cudahy neighborhood near Milwaukee, presumed to be the residence of the gunman. Generators and floodlights were set up along the street and a bomb squad was on the scene.
The names of the victims were not made public pending notification of relatives, although members said the president of the congregation and a priest were among the victims.
Oak Creek police chief John Richards told CNN the gunman "lived in a community neighboring ours, we're doing a 24-hour backcheck, just to get any idea what he was up to, what he was doing.
"Right now there is no indication that there were any red flags."
The wounded police officer had been shot eight or nine times in the face and extremities at close range with a handgun. None of the wounds were life-threatening, Edwards said.
A search of the Lexis-Nexis online records service showed that Page had lived at at least 20 addresses in Wisconsin, North Carolina, Colorado, California and Texas.
Authorities said the gunman had used a 9mm semi-automatic pistol, which was recovered at the scene. They were trying to track the origin of the weapon.
Wisconsin has some of the most permissive gun laws in the country. It passed a law in 2011 allowing citizens to carry a concealed weapon.
Jagjit Singh Kaleka, the brother of the president of the temple, who was among the six Sikhs killed, said he had no idea what the motive was for the attack.
The shooting came just over two weeks after a gunman killed 12 people at a theater in Aurora, Colorado, where they were watching a screening of new Batman movie "The Dark Knight Rises."
The September 11 attacks were carried out by Muslims linked to the al Qaeda militant group led by Osama bin Laden. Sikhs are not Muslim but many Americans do not know the difference, members of the Sikh community said.
There are 500,000 or more Sikhs in the United States but the community in Wisconsin is small, about 2,500 to 3,000 families, said local Sikhs.
The Sikh faith is the fifth-largest in the world, with more than 30 million followers. It includes belief in one God and that the goal of life is to lead an exemplary existence.
The temple in Oak Creek was founded in October 1997 and has a congregation of 350 to 400 people.
(With Reuters and PTI inputs)