BEIJING — Police investigating the stabbing death of the father of a former U.S. Olympian said today the suspect was distraught over family problems. Chinese authorities unsettled by the attack during the Beijing Olympics tightened security at tourist spots around the city.

Wang Wei, vice president of the Beijing Olympic organizing committee, said Sunday that security in and around Olympic venues was already sufficient but would be increased at scenic spots around the city.

He said Chinese investigators and U.S. Embassy officials believe Saturday's attack was "an isolated incident" and suggested such random acts are difficult to prevent. There was no indication the assailant knew his victims had any connection to the games, according to Olympic and Chinese authorities.

"Beijing is a safe city, but unfortunately we are not immune to violent acts," Wang told reporters.

Todd and Barbara Bachman of Lakeville, Minn. — parents of 2004 volleyball Olympian Elisabeth "Wiz" Bachman and in-laws of U.S. men's volleyball coach Hugh McCutcheon — were attacked by a Chinese man while visiting the 13th-century Drum Tower on Saturday. The assault came hours after the games' spectacular opening ceremony.

The U.S. Olympic Committee confirmed Bachman died from knife wounds and Barbara Bachman suffered life-threatening injuries. She and their Chinese tour guide, who was also injured in the attack, were being treated in a Beijing hospital.

The committee said Sunday that Mrs. Bachman suffered multiple lacerations and stab wounds. She underwent eight hours of surgery and was in critical but stable condition.

Rob Browning, leader of the men's volleyball team, said the team was united in supporting the Bachmans.

"We are absolutely devastated by what has occurred, for their loss and for everything they are going through," Browning said. "We are a family, and we'll get through this together as a family."

President Bush, in the Chinese capital to attend some Olympic events and meet with Chinese leaders, thanked President Hu Jintao on Sunday for his government's handling of the attack.

"Your government has been very attentive, very sympathetic, and I appreciate that a lot," Bush said.

Hu said his government took the incident "very seriously" and pledged to keep Washington apprised of the investigation.

Elisabeth Bachman was with her parents at the time of the attack, but was uninjured. Her father was chief executive officer for Bachman's, Inc., a home-and-garden center based in Minneapolis.

Shortly after the attack, the assailant, Tang Yongming, 47, leapt to his death from a balcony on the Drum Tower, five miles from the main Olympics site, the official Xinhua News Agency reported.

Violent crime against foreigners is rare in tightly controlled China, and the assault occurred despite major security measures that have blanketed the capital city during the Olympics. A 100,000-strong security force plus countless volunteers have been deployed to protect against any trouble.

Police said Tang went through his second divorce in 2006 and grew increasingly despondent when his 21-year-old son started getting into trouble, Xinhua reported. The son was detained in May 2007 on suspicion of fraud, then received a suspended prison sentence in March this year for theft.

Associated Press writers Paul Alexander, Jimmy Golen, Audra Ang and Charles Hutzler contributed to this story.