STOCKHOLM (AP) — Four chimpanzees escaped from their enclosure in a Swedish zoo and roamed freely before being captured and euthanized on Wednesday, according to Swedish media.

Annika Troselius, press spokeswoman for the group that operates the Furuvik zoo, told the Expressen daily that the animals had to be euthanized because there was not enough tranquilizer for all of them.

She said that the chimpanzees are strong and dangerous animals and the zoo’s main focus “is that no human gets hurt.”

Troselius told Swedish radio that a fifth chimpanzee is believed to have left its enclosure, though there were no other immediate details.

It was unclear how the mammals were able to escape from their enclosure.

The Furuvik zoo is located near Gavle, 165 kilometers (100 miles) north of Stockholm, and had seven chimpanzees. It is part of an amusement park. According to the park’s web page, it is also the only primate research station in the Nordic countries.