新聞背景：美國警方今天向媒體提供的一些材料表明，制造4月16日清晨槍擊血案的韓裔學生趙承熙患有一定程度的心理疾病。資料顯示，韓裔學生趙承熙于2005年曾經在弗吉尼亞理工大學先后兩次圍堵兩名女性而被警方拘訊，自那時候起，警方和他有了聯系。警方還說，自那時起，一位同伴發現他有自殺傾向，為此帶他進行過心理咨詢和治療。

Video:Gunman kills 32 students in Virginia school

Bush expresses sympathy at Va. Tech convocation

New evidence is emerging about the student who killed 32 people Monday at Virginia Tech University. Police say the gunman was previously accused of stalking two female students, and acquaintances expressed concern that he might be suicidal. NBC News says it received a package Wednesday containing pictures of the shooter brandishing handguns, a video and some writings. Virginia police called the package a "critical component" of its investigation. VOA's William Ide has more from Washington.

Virginia Tech Police Chief Wendell Flinchum says authorities met with Cho Seoung-hui on two separate occasions in 2005, after his phone calls, e-mails and contacts with two women raised concerns.

In both incidents, police say, they spoke with Cho, a 23-year-old student at the university. But they say he did not make any threats. One of the women who filed a complaint against Cho told police that he was "annoying," but neither of the two women pressed charges.

Authorities say Cho was also referred to the school's disciplinary system. University officials did not comment on whether any action was ever taken against Cho.

In December 2005, police chief Flinchum says, acquaintances called police.

"Our department received a call from an acquaintance of Cho, who was concerned that Cho might be suicidal," he said. "Officers again met with Cho and talked with him at length. Out of concern for Cho, officers asked him to speak to a counselor. He went voluntarily to the police department. Based on that interaction with the counselor, a temporary detention order was obtained, and Cho was taken to a mental health facility."

Flinchum says police heard nothing more after that.

"Since those contacts in November and December of 2005, more than a year ago, I am not aware of any additional incidents or reports that were made to our department," he said.

Mental health officials at the university say they are vigilant about monitoring students who might turn violent, but also note that that can be difficult to predict.

"Clearly, if anyone had any warning of a violent incident people would have stepped in and acted," said campus counselor Chris Flynn. "This university is extremely proactive at meeting and discussing students of concern."

As the nation continues to mourn the tragedy, leaders from around the world sent condolences.

Among those killed in Monday'sshooting rampagewas Liviu Librescu, a engineering and math professor, and Holocaust survivor, who is being called a hero for his action to protect his students from the gunman.

President Bush noted his sacrifice, during a speech Wednesday at the U.S. Holocaust Memorial Museum in Washington, which is marking the National Days of Remembrance of the Holocaust.

"With the gunman set to enter his class, this brave professor blocked the door with his body, while his students fled to safety," he said. "On this day of remembrance, this Holocaust survivor gave his own life so that others may live."

Virginia Governor Tim Kaine said Tuesday he will appoint an independent panel of law enforcement experts to evaluate whether Virginia Tech reacted appropriately to the shootings.