A threatening note found aboard a Washington-to-New York Amtrak (search) train prompted police to detain it for an hour and a half Thursday morning while they checked all passengers for identification and examined the overhead luggage racks.

After officers videotaped the passengers and searched the cars with at least one bomb-sniffing dog, the train was declared safe and allowed to leave Newark Penn Station (search) to continue on its way.

Amtrak spokesman Dan Stessel said he did not know the exact contents of the note, but a law enforcement source said it contained "pro-Muslim, anti-Jewish rhetoric." The note included the phrase, "You're all sitting ducks," said the source, who spoke on condition of anonymity.

The note was attached to the mirror in a restroom of the train's cafe car, Stessel said. The passenger who found it notified the train crew, and police were waiting for the train when it reached Newark, its next scheduled stop.

Passengers were not told what was going on as the train was held in the station shortly after 8 a.m.

Transit police asked to see each passenger's identification and checked the information with small hand-held computer devices, said Terry Taylor, The Associated Press' sports editor, who was on the train. Police swept overhead luggage compartments with a metal wand, and at least one police dog was brought aboard.

The train left the station at 9:30 a.m. No explanation was given to passengers.

The note was to be sent to a crime laboratory, Stessel said.

New Jersey authorities have stepped up patrols on trains since the March train bombings in Spain that killed nearly 200 people.

Rail officials last week announced that more security measures will be imposed on New York-bound trains during the Republican National Convention (search) in New York at the end of the month.