PITTSBURGH -- Police are investigating whether a deputy was justified in shooting and killing a dog in Pittsburgh's North Side.

The owners of Lincoln, a 10-month-old pit bull, said he was docile and playful, not violent.

Tara Mangan said an Allegheny County sheriff’s deputy knocked on her door in Brighton Heights Thursday afternoon to deliver tax documents to her upstairs neighbor.

She said she directed him to the French doors on the side of the house. Moments later, she said she heard a gunshot and found Lincoln dead in the back yard.

“There is no misunderstanding,” said Mangan. “He shot my dog maliciously."

Mangan said the deputy's story that Lincoln tried to attack him doesn't add up.

"The leash doesn't go past where he shot him at. He can't go any farther; he was in his own back yard, secure, on a leash," said Mangan.

The deputy said he couldn’t see the leash.

Allegheny County Sheriff’s Chief Deputy Joseph Rizzo said in a statement, "If, in any event, a Sheriff’s deputy goes to a house and there is an aggressive animal, they make every effort to get out of harms way. If a dog is going to attack the deputy, they have no recourse."

Mangan said she feels the deputy should be punished and should have to apologize to her children.