One Humboldt penguin was found dead in the flamingo cage and two of its companions had mysteriously vanished, a police spokesman said on Tuesday in the northwestern German city.

It is the latest in a string of mysterious incidents at the Dortmund Zoo, including one other death and several disappearances, although authorities have not yet determined if there is a link.

In November, the 21-year-old sea lion Holly was found with her skull smashed in and three teeth missing.

Authorities investigate

Police believe Holly was killed by an intruder, although this suspicion has not yet been corroborated. The zoo itself has ruled out the possibility of an accident.

In August, several pygmy marmosets and two acouchi rodents disappeared without a trace.

Authorities are trying to determine if the two missing penguins were stolen or somehow escaped on their own.

blc/jm (AP, dpa)