The alleged shooter intended to kill Congresswoman Gabrielle Giffords when he pulled the trigger of a pistol in a shooting spree which also claimed lives of five others including U.S.District Judge John Roll at a supermarket in northwest Tucson, Arizona Saturday morning, officials said.

Jared Lee Laughner, 22, was named as the suspect in one of America's gravest murders in recent years. He was described by Pima County Sheriff Clarence Dupnik as one with a criminal record and one with mental issues.

The gunman used a Glock 19, a semi-automatic pistol that was legally purchased on Nov. 30 at Sportman's Warehouse in Tucson, local law enforcement sources said, according to the Washington Post.

Dupnik was "not convinced" that the suspect acted alone, he said, but he refused to comment further.

However, the sheriff said the incident is not terrorism-related, and the authorities are seeking second person.

Six people, which also included Gabrielle Giffords' senior aide and a 9-year-old girl were shot to death by the suspect. The aide was identified as Gabe Zimmerman, 30, Giffords' community outreach director who was engaged to be married.

At least 12 others were wounded during the horrifying rampage which occurred at 10:00 p.m. local time when Congresswoman Giffords was participating in her first public event since being re-elected to U.S. Congress in November 2010.

President Barak Obama said the authorities have launched a "comprehensive investigation", and he has ordered FBI Director Robert Mueller to go to Arizona and coordinate the investigation.

The suspect is described by a number of media outlets as a troubled youth, who has posted anti-government messages on YouTube and MySpace, voicing his distrust of the establishment and suggested that anyone can call anyone a terrorist.

"Goodbye," Loughner said in a message posted on his MySpace account at approximately five a.m. Saturday. "Dear friends ... Please don't be mad at me."

"I can't trust the current government because of fabrications,"Loughner wrote in the YouTube message. "The government is implying mind control and brainwash on the people by controlling grammar."

The man, who posted his self-portrait on the internet, also mentioned his concern over literacy rates and the fact that nobody speaks English. In a video, the man spoke with British accent.

He also posted pictures including one about his volunteering in a book show.

Congresswoman Giffords was shot at close range by the gunman when she was greeting constituents at a campaign event called "Congress on Your Corner."

As as result, security measures for U.S.senators and congessmen have been beefed up. Related measures to deal with future incidents will be in place, authorities said.

Giffords served at District 8, which includes a 114-mile (182-kilometer) stretch of the U.S. border with Mexico.

A mild Democrat, Giffords was first elected to U.S.Congress in 2006. She won in re-election to her third term last November.

During last year's campaign, Giffords touted her efforts to push the Obama administration to deploy National Guard troops to the border and for playing an instrumental role in securing 600 million dollars in funding to add more technology and Border Patrol agents.

A glass panel at her Tucson office was shattered the day after the vote. Spokesman C.J. Karamargin told CNN then that staffers suspected someone shot a pellet gun at the glass.

Giffords opposed SB 1070, the state's new controversial immigration law which makes it illegal for aliens being in the United States without proper papers, calling it "divisive" and supported instead comprehensive immigration reform at the national level, local newspaper Arizona Republic reported.

Giffords was a member of the Arizona House and Senate before going to Washington.