NOVATO (CBS SF) — More than 100 cats and kittens have been dumped off at a North Bay shelter in a series of anonymous, late-night visits, overwhelming shelter operations.

The Marin Humane Society says the latest happened on Monday, with surveillance video showing a group of people pulling up to the Novato facility and leaving behind two dozen cats in cardboard boxes.

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All the cats and kittens appeared to be related to previous ones left behind three other times in the same manner; almost all of them are black and white “tuxedo” cats. The surveillance footage shows the same vehicle used in the previous dump-offs, a total of four times over the past year and a half.

“This is a lot of stress on our shelter,” said Marin Humane Society spokeswoman Lisa Bloch. “We’re really inunadated. We have as twice as many cats as we normally do.”

Bloch said there was no crime and no one will be in trouble for dumping off the cats, but any information could help workers end the overbreeding.

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“Perhaps it’s a hoarding situation. So it’s important we get that person some help,” said Bloch.

In a statement, Director of Customer Services Keri Fennell said it’s clear the hearts of those who dropped off these animals are in the right place. “However it’s important we find out where these cats are coming from so that we can offer assistance including spaying and neutering so this overbreeding doesn’t continue to happen.”

The shelter said workers have been extremely busy vaccinating , spaying/neutering and microchipping the cats in addition to performing their normal duties.

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To help alleviate the now overcrowded conditions, the shelter is waiving the adoption fee for all cats and kittens until the end of August.