The gunman who killed three women in an aerobics class at a Pittsburgh-area gym bought accessories for his weapons from the same dealer that sold a gun to the Virginia Tech shooter.

George Sodini, 48, purchased the items from TGSCOM Inc. of Green Bay, Wis., before committing the Aug. 4 massacre that left three women dead and nine wounded. He then killed himself.

It wasn't immediately clear what accessories Sodini bought.

Seung-Hui Cho purchased a .22-caliber handgun from TGSCOM in February 2007, two months before he killed 32 people at Virginia Tech.

Police investigating Tuesday's shootings at the L.A. Fitness center in Collier Township, Pa., say Sodini obtained his weapons legally.

TGSCOM's president, Eric Thompson, confirmed Sodini's purchases after WPXI-TV in Pittsburgh obtained a receipt. Thompson said he's cooperating with investigators.

Meanwhile, police say Sodini called his mother before the shootings to tell her of his plans, WPXI reported.

"I'm going to kill a bunch of people. I don't expect I'm going to survive this," police say he told her, according to the station. Her response wasn't disclosed.

Sodini entered the gym Tuesday and went into a Latin dance class at about 8:15 p.m. in black workout gear. He turned off the lights and fumbled around in a duffel bag before taking out three guns and firing indiscriminately.

Police described Sodini as a misogynist and said he didn't know his victims.

Killed were Heidi Overmier, 46, of Carnegie, a sales manager at an amusement park; Jody Billingsley, 37, of Mount Lebanon, who worked for a medical-supply company; and Elizabeth Gannon, 49, of Pittsburgh, an X-ray technician at Allegheny General Hospital. About 75 people attended a vigil to remember them Thursday night in downtown Pittsburgh.

In his 4,000-word blog apparently dating back almost a year, Sodini complained about his wrongful rejection by "30 million" American women and alluded to his plans to commit a mass shooting.

Mental health experts say Sodini shared a chilling trait with other spree killers: the desire to make their woes understood through multiple deaths.

Sodini did not appear to have any documented mental problems, but his massacre shares threads with others analyzed by psychiatrists and legal experts.

"They're thinking, 'I want everyone to understand and appreciate why I'm doing this,' and the way to do that, in their mind, is to kill other people and not just themselves," New York attorney Carolyn Wolf, whose firm specializes in mental health issues, told The Associated Press Thursday. "In their mind it sends a broader message."

Cho, who committed suicide after the Virginia Tech massacre, also left behind an online journal and posted YouTube videos. Prior to his rampage, he sent a video tirade to NBC railing about being overlooked by "snobs" and rich "brats."

"These people get into a very self-centered, sometimes self-aggrandizing, often psychotic path that enables them, in their mind, to finally get the attention they crave," Wolf said.

Many mass murderers feel rejected by a "pseudo community" that may exist only in their minds, said Dr. James Knoll, a forensic psychiatrist at the State University of New York's Upstate Medical University in Syracuse.

"He probably worked out at this gym, he was tanning and working out, trying to improve himself," Knoll said of Sodini. "These are things he thought would get him a relationship. It wasn't working."

In his Web diary, Sodini wrote that his anger stemmed from unfulfilled desire: The women at his gym "look so beautiful as to not be human," he wrote.

Two undated videos apparently recorded by Sodini were posted online showing him touring his home and talking about hiding his feelings, trying to "emotionally connect" with people and struggling to impress women.

Click here to watch the videos.

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The Associated Press contributed to this report.