PHILADELPHIA (AP)  -- The search for a third suspect in the weekend slaying of a city police officer continued Monday as authorities followed a tip that the man may have been spotted aboard a train bound for Manhattan.

A passenger aboard a New Jersey Transit train called 911 around 9 a.m. to report that a man matching the description of Eric Floyd, 33, was on board. Floyd is wanted in the fatal shooting of Sgt. Stephen Liczbinski following a bank robbery on Saturday morning.

Police searched the train and areas near the tracks in Elizabeth and Newark, N.J., but did not find Floyd, NJ Transit spokesman Dan Stessel said. Train traffic was halted as police searched the area, but it resumed around 11:20 a.m.

In Philadelphia, Deputy Commissioner William Blackburn said authorities would review video from a train station platform. ``We're aggressively pursuing leads,'' Blackburn said. ``We're basically trying to hunt this guy down.''

Investigators believe Floyd had escaped from a halfway house in Berks County.

Philadelphia officials also announced that the reward for information leading to Floyd's arrest had grown to more than $100,000. Mayor Michael Nutter urged Floyd to turn himself in and warned that anyone who helped him would be prosecuted to the fullest extent of the law.

``It is time to face up to what you have done,'' Nutter said in a plea to Floyd. ``We can do this the easy way or we can do this the hard way.''

One suspect, Howard Cain, 33, was shot to death by police during a chase after the robbery. Another man, Levon Warner, 38, was arrested and charged Sunday with murder, robbery, conspiracy and related offenses.

District Attorney Lynne Abraham also said Monday that she believed the assault rifle used to kill Liczbinski had been purchased at a gun show in Fayetteville, N.C., in 1996. She warned Floyd that the FBI and police across the country were looking for him.

Liczbinski, a 12-year veteran who would have turned 40 on Tuesday, was shot responding to the robbery in northeast Philadelphia around 11:45 a.m. Saturday. The suspects fled the robbery and opened fire after Liczbinski confronted them a short distance away, shooting the officer at least five times, police said.

Officials have also announced a memorial fund for his family; he was a married father of three.

Liczbinski is the third Philadelphia police officer slain on duty in the past two years.

Officer Chuck Cassidy, 54, was killed during the botched robbery of a doughnut shop in the city's West Oak Lane neighborhood on Oct. 31. The alleged gunman was arrested at a homeless shelter in Miami days later and is awaiting trial.

In May 2006, Officer Gary Skerski was fatally shot in the neck when a man robbing a bar fired a shotgun out the back door. His killer, Solomon Montgomery, pleaded guilty to first-degree murder and was sentenced to life in prison.