(Photo Credit: AP Photo)

The manhunt for a "cop killer" was expanded today to a nationwide dragnet to find the suspected bank robber who fatally shot a Mississippi police officer two days before Christmas, according to the FBI.

Tupelo Police Department officer Gale Stauffer and another officer were hit by gunfire Monday when they confronted suspected bank robbers during their getaway in the city.

As the officers approached suspects in a vehicle, which was stuck in traffic at a railroad crossing, at least one of the suspects opened fire at close range, according to an account posted online at the Officer Down Memorial Page.

The suspects fled, leaving Stauffer fatally shot and another officer critically wounded.

Stauffer "has made the ultimate sacrifice for his community," Tupelo Mayor Jason Shelton said, urging the public to help "so that the criminal or criminals responsible for this horrendous act can be brought to justice."

After reviewing bank surveillance video from the robbery of a BancorpSouth bank in Tupelo, authorities are looking for a thin, possibly African-American man with light complexion, standing between 5-feet-9 and 6-feet tall, according to the Mississippi Department of Public Safety.

The suspect seen in the surveillance video was wearing khaki or cargo-style pants, white Converse tennis shoes, a long-sleeved jacket and a blue ski mask, the state public safety department said. A charcoal-colored, medium-sized sedan might have been used as a getaway car.

As part of the investigation, authorities also released a photo (shown below) of a "person of interest" standing in what appears to be a convenience store minutes before the robbery at the bank. Police did not discuss any possible connection to the bank shooting.

(Photo Credit: Mississippi Department of Public Safety)

More than 100 agents, officers, deputies and marshals worked through Christmas to track down the suspects, an FBI official said.

The FBI, BancorpSouth and others are offering more than $152,000 for information leading to an arrest in the case. Anyone with information is asked to call the FBI's tip line at 1-800-CALL-FBI (1-800-225-5324).

Stauffer was a combat veteran of the Louisiana Army National Guard, and he had served with the Tupelo Police Department for eight years, according to the Officer Down Memorial Page.

He was married with two young children, the memorial page said.

ABC News' Ben Krolowitz contributed to this report.