A Britsh Al Qaeda operative conducting surveillance on U.S. soil in 2000 favored using a limousine packed with explosives or a hijacked oil tanker truck to attack financial institutions in Manhattan and New Jersey, police officials said.

"The most obvious technique to utilize, that comes to mind ... would be a limousine in the VIP underground car park," the operative, Dhiren Barot, wrote in a memo about the Prudential Building in Newark, New Jersey.

Barot was sentenced to life in prison was sentenced to life in prison in Britain last week after pleading guilty to conspiring to commit mass murder.

In his memo, Barot also suggested that "arson may be the best choice" and advised "ramming trucks (oil tankers, etc.) straight through the glass front entrance into the lobby area."

Hijacking a truck "will probably be much easier here in New Jersey than in New York since there is less security and no tunnels to pass through," added Barot, who spied on one location while sitting at a nearby Starbucks coffee shop.

The memo was quoted during a New York Police Department briefing Thursday on terror threats for private security officials from Wall Street firms and other businesses. The memo and briefing shed more light on the designs of Barot.

Prosecutors in Britain said Barot shelved the plan to attack the U.S. financial industry targets after Sept. 11, 2001, and instead focused on using limousines loaded with gas, napalm and nails to attack landmark London hotels and railway stations.

The proposals for the strikes in Britain and for those against the Prudential Building, the International Monetary Fund in Washington and the New York Stock Exchange and the Citigroup headquarters in New York were sent to Al Qaeda leadership like "corporate reports going to head office," a British judge said.

Investigators said they uncovered some of the evidence stored on computers seized at the home of an Al Qaeda computer expert in Pakistan in July 2004, prompting the NYPD to heighten security around the city.

During his reconnaissance mission in the summer of 2000, Barot became fixated on the black sedans regularly used by corporate executives, according to an NYPD analyst citing the computer evidence.

Barot noticed the chauffeured cars were given easier access to parking in and around corporate offices, a security lapse that enhanced the potential for a car bomb.

The operative "picked up on that — preferential treatment given to the black cars of the corporate officers," an NYPD analyst, Peter Patton, told the private security officials.

Barot shot video and took extensive notes while patiently assessing the buildings, the analyst said.

"He sat in a Starbucks for days just looking at one target," he said. "He was just looking at his target, trying to figure out the best time to conduct an attack that would result in the most casualties."

In one instance, he noted, "The guards are a combination of male and female. The uniform is that of blazer, white shirt and trousers. They all carry wireless radios. Impersonating one would not be difficult, but it would be very hard to fool the other guards."

Patton said Barot considered trying to rent office space in one of the buildings to ensure easy access. His notes show he also was drawn to targets with vast expanses of glass — a legacy of the Al Qaeda attacks on U.S. embassies in Africa.

"One of the lessons learned after the 1998 embassy bombings was that 80 percent of the casualties were caused by flying glass," Patton said.