Thomas Frank

USA TODAY

Several experts including a former New York City police commissioner said Sunday the explosion that injured 29 people on a Manhattan street was clearly an act of terrorism, and they were perplexed that Mayor Bill de Blasio called it only "an intentional act."

"It is absolutely an act of terrorism. I couldn't disagree with him (de Blasio) more," Howard Safir, who was police commissioner from 1996 to 2000, said in an interview. "I think they do a disservice to the public when they try to sugar coat something that is a horrific act."

He said people should realize this is a new era. "As we are more successful on the battlefields in the Middle East, our adversaries are looking for a target," Safir said.

Jerome Hauer, a former commissioner of the New York State Division of Homeland Security and Emergency Services, said de Blasio might be trying to maintain public calm by not calling the explosion a terrorist attack, "but it's certainly an act of terrorism."

New York Gov. Andrew Cuomo said Sunday there is “no evidence of an international terrorism connection” and appeared to hedge in characterizing the explosion Saturday night in the Chelsea neighborhood of Manhattan.

“It depends on your definition of terrorism. A bomb exploding in New York is obviously an act of terrorism, but it’s not linked to international terrorism. In other words, we find no (Islamic State) connections,” said Cuomo, a Democrat.

Authorities: NYC footage shows person moving devices before blast

No individual or group has publicly claimed credit for the explosion, which occurred around 8:30 p.m. Saturday on a bustling, restaurant-lined street in the largely residential neighborhood. It was caused by a homemade device. A second device believed to be a pressure cooker with wires and cellphone was later found four blocks away and was safely removed early Sunday.

Experts said Sunday that the explosion meets the principle federal definition of "domestic terrorism," which was added to federal statutes by the USA Patriot Act shortly after the 9/11 attacks. Federal law defines domestic terrorism as "acts dangerous to human life" that appear intended to "intimidate or coerce a civilian population" or to influence government policy.

"It seems to meet the bar of the FBI's definition," said Frank Cilluffo, a former special assistant for homeland security to President George W. Bush who now directs the Center for Cyber and Homeland Security in Washington, D.C. "We still don’t have all the information here and don’t know specifically what motivated the individual. But clearly it was pre-meditated. Clearly it was targeting innocent civilians."

Other parts of federal law define "terrorism" slightly differently. A "federal crime of terrorism" is defined as an "offense" that is "calculated to influence or affect the conduct of government by intimidation or coercion, or to retaliate against government conduct." The definition says nothing about civilians.

In the section of federal law dealing with foreign relations, "terrorism" is defined as "premeditated, politically motivated violence" undertaken by "subnational groups" against civilian targets.

Officials have previously been cautious in declaring attacks to be acts of terrorism. In December, the day after a married couple of Pakistani-descent in San Benardino, Calif., killed 14 people in a mass shooting, the agent in charge of the FBI's Los Angeles field office would not call the attack an act of terrorism.

"It would be irresponsible and premature of me to call this an act of terrorism," David Bowdich told the news media then. "The FBI defines terrorism very specifically, and we are still — that is the big question for us. What is the motivation for this?"

The FBI quickly declared the attack terrorism. The couple was killed shortly after the attack in a shoot-out with police.

Experts said de Blasio, a Democrat, might be refraining from calling the explosion terrorism until authorities know more about the attackers. Motivation is irrelevant to whether an attack involves terrorism, they added.

"Whether or not it’s somebody who's angry at the government or somebody who has come back from Syria or somebody who has been radicalized on line, it’s still terrorism and it’s going to create this angst in people," Hauer said. "I think the world of Bill de Blasio. But this was clearly terrorism."

More on the blast in New York City: