Rejecting new gun control laws, Mitt Romney said the answer to horrific acts of violence may be “changing the heart of the American people.”

In London for the opening of the Olympics, Mr. Romney spoke on Wednesday to NBC News, the broadcaster of the Summer Games. The network showed excerpts from the interview on “NBC Nightly News” and posted the rest online.

Asked if he thought it was time to look anew at controlling access to assault weapons after last week’s mass shooting in Aurora, Colo., or to limit an individual’s right to buy thousands of rounds of ammunition, Mr. Romney repeated his position that the country did not need more gun-control laws.

Americans “sometimes hope that just changing the law will make all bad things go away,” Mr. Romney said. “It won’t. Changing the heart of the American people may well be what’s essential, to improve the lots of the American people.”

Mr. Romney’s campaign Web site explains his position on gun control: that the country has all the laws it needs and that it should focus on enforcing them to punish those who use firearms to commit crimes.

Mr. Romney said in the interview that the suspect in the Colorado rampage, James E. Holmes, whom the police have accused of killing 12 and injuring 58, was illegally in possession of weapons. “Well, this person shouldn’t have had any kind of weapons and bombs and other devices, and it was illegal for him to have many of those things already,” Mr. Romney said. “But he had them.”

Officials have said the three guns used in the mass shooting were bought legally. A spokesman for Mr. Romney, Ryan Williams, said he was referring specifically to what the police identified as homemade incendiary devices in the suspect’s apartment, which are illegal in Colorado, not to firearms.

Mr. Romney, who will attend the Olympics opening ceremony on Friday, side-stepped a question about the horse that is co-owned by his wife, Ann, and competing in the elite sport of dressage.

“For those of us who don’t follow the sport, what happens?” he was asked.

“I have to tell you, this is Ann’s sport,” Mr. Romney said, declining to even utter “dressage,” a French word meaning “training” and sometimes described as horse ballet.

“I’m not even sure which day the sport goes on,” Mr. Romney said. “She will get the chance to see it; I will not be watching the event. I hope her horse does well.”

Mr. Romney has a busy day of meetings on Thursday and what the British news media calls “photo sprays” with political leaders, including former Prime Minister Tony Blair and current Prime Minister David Cameron.