New Orleans police say they didn't anticipate a vehicular attack would thwart their security measures

New Orleans police said they did not anticipate that a vehicular attack would thwart their security measures, after the driver of a pickup truck drove around a police car that was parked to block access to Bourbon Street, up onto a sidewalk and then plowed into scores of New Year's revelers in a deadly attack.

"It wasn't something we expected to account for," New Orleans Police Capt. LeJon Roberts told reporters during a press briefing on Wednesday when asked if they anticipated a vehicle driving onto the sidewalk to get around the parked police car.

The driver of a rented Ford F-150 Lightning truck rammed into and through the crowd early Wednesday, killing at least 15 people and injuring dozens of others, officials said. The suspect was fatally shot by police after opening fire on law enforcement, police said.

Protective bollards were being replaced

Protective posts known as bollards, which are designed to block traffic, were in the process of being replaced on Bourbon Street ahead of the city hosting the Super Bowl this year, according to New Orleans Mayor LaToya Cantrell. The previous bollards were deemed ineffective by police and removed, and the replacements were not yet up ahead of Wednesday's attack, she said.

A police cruiser was parked at the intersection Wednesday to block vehicle access to Bourbon Street, though the suspect in the deadly attack drove around the vehicle and onto the sidewalk, police said.

Graphic video showed the truck turn off Canal Street and drive around the police car blocking the road, and into the crowd.

New Orleans Police Chief Anne Kirkpatrick said that police had been "aware of the bollard situation" and took steps to “harden those target areas" where the bollards were with patrol cars, barriers and officers.

"We did indeed have a plan but the terrorist defeated it," Kirkpatrick said during a press briefing on Wednesday.

In a statement Wednesday, the city said New Orleans installed bollards at key locations along Bourbon Street in 2017 to block vehicles from entering the famed throughfare whenever needed.

"The black removable bollards previously installed at key locations along Bourbon St. proved unreliable and have been non-operational. In the interim, white gate barriers have been used in these areas, managed by the New Orleans Police Department (NOPD) to secure the street and regulate vehicle access for safety purposes," the statement said.

Construction on the Bourbon Street Bollard Assessment & Replacement Project began in November and is scheduled to be completed in February, according to the New Orleans Department of Public Works website, which also features conceptual images of the completed project, which will feature "removable stainless-steel bollards."

"The City of New Orleans is committed to ensuring the safety and functionality of Bourbon Street," the city said in Wednesday's statement.

Louisiana Gov. Jeff Landry said Wednesday that the suspect was "evil" and could have "easily" attacked pedestrians on Canal Street, and said they are going to assess the security measures in place.

"We intend to be transparent in assessing any defects that may have existed in the system so that we can address them. It's the only way to ensure that any mistakes that were made are corrected," he told reporters during Wednesday's briefing.

'There's a failure here, there's no question'

In the weeks leading up to the holidays, federal law enforcement and intelligence agencies warned police around the country that low-tech vehicle-ramming was a key area of concern and that they needed to prepare for such a possibility.

Former NYPD Chief of Detectives Robert Boyce called the apparent security lapse in New Orleans "unacceptable."

"There's a failure here, there's no question, there's a security failure," he told ABC News on Wednesday. "If he defeats that car and pops up on the sidewalk, why wasn't there some device there? You could put a cement block there, for that matter, in temporarily until you get your bollards fixed."

Boyce said that after a deadly sidewalk incident involving a vehicle in New York City in 2017, police placed cement barriers on sidewalks until bollards could be installed.

Donald Mihalek, a former senior official with the Secret Service, said that garbage trucks or other types of large vehicles have been used to secure an event perimeter.

"In this day and age, event security is taking on a new dynamic because of the terrorism threat," he told ABC News on Wednesday, noting that a vehicle-borne attack is one such threat that needs to be considered when planning event security.

"When it comes to threats these days, failing to imagine a threat is not planning for the threat," he said.

New Orleans City Council President Helena Moreno told "Good Morning America" Wednesday that the city council questioned during a recent meeting why the construction on the Bourbon Street bollard project wasn't already completed.

"Obviously, a lot of different things were said about delays and contractors," she said. "But it's like, this construction should have happened much earlier and everything really should have been ready and in place, fixed, repaired, ready to go now, well in advance of the Super Bowl."

An act of terrorism

The FBI said the New Year's Day truck ramming attack was being investigated as an act of terrorism.

The suspect killed in the attack was identified by the FBI as 42-year-old Shamsud-Din Jabbar, an Army veteran from Texas.

A motive remains under investigation. An ISIS flag was attached to the pickup's rear hitch, according to the FBI, which is trying to assess whether the suspect had any connection to terror groups.

Investigators believe the suspect did not act alone and are working to track down any known associates of Jabbar's, the FBI said.

Improvised explosives devices (IEDs) and other weapons were found inside the pickup truck used in the attack, the FBI said. Two additional IEDs were discovered in the French Quarter and rendered safe, the FBI said.

Crude pipe bombs stuffed with coils and nails were found at the scene along with a grenade, sources said.

"He was hell-bent on creating the carnage that he did," Kirkpatrick said.

ABC News' Dominick Proto contributed to this report.

This story has been updated for clarity.