"We are treating this as a hate crime due to the nature of the graffiti on the vehicles," police spokesman Louis Heroux said Tuesday.
The vandalism was first noticed after a fire alarm sounded in the apartment on Monday evening in the city's Notre-Dame-de-Grace borough.
Heroux said firefighters didn't find any fire, but noticed that some vehicles in the garage had been vandalized.
Red swastikas were spray painted on their hoods and the windshield of one vehicle had been smashed.
Harvey Levine, the Quebec regional director of B'nai Brith Canada, said a witness told him the vandalism went further.
"In this particular case, not only were the cars targeted with swastikas, but there was a letter that was placed on four cars with a swastika on it," Levine said.
"When one of the letters was opened by police, there was a bullet inside and there was a note ...." He said it warned about getting a bullet in the head.
Levine said one envelope was opened in the presence of people who were in the garage and then the other unopened ones were taken to the police station.
The B'nai Brith official said he did not see the letter, but was told about it by one of the car's owners.
Heroux would not confirm the existence of the envelopes.
"There is evidence that was found on site that will help in the investigation, but we can't get into details about what was found," Heroux said.
He added that crime scene technicians took pictures and collected information that will help them in their investigation.
Levine said a number of Jews live in the area and there is also a synagogue there as well.
He called the incident "deplorable."
"A particular problem like this is not some teenager running around with a spray can, this is a pre-meditated, hate-motivated crime." Levine said. "I certainly hope the culprits will be apprehended and when they are apprehended, I hope that they will be charged with a hate crime because this is very significant."
Levine said while the swastikas on the vehicles appear to be backwards, it's not uncommon for young people to mix up the symbol with the one traditionally used by the Nazis.
The hate-motivating message is still usually apparent, Levine said.
"They are just confused on how the swastikas are actually supposed to look," he added.
Police have not made any arrests.
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