The vicious attack unfolded just a few feet inside the park at East 106th Street and Fifth Avenue on Saturday night around 8:30 p.m.
Police said a couple, a 51-year-old man along with a 43-year-old woman, were walking their two dogs, a chihuahua and Eli, a pit bull German shepherd mix. Both animals were on a leash.
The suspect, with his three dogs, possibly pit bull terriers, were off-leash. Witnesses said the suspect's dogs started biting the victim's dogs, and there was an argument with the woman trying to separate the pack.
In a flash, the suspect allegedly pulled out a switch blade and repeatedly stabbed Eli.
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"There was a dog on the ground that was dead, a lot of blood around it, a guy was trying to do something - and three other pit bulls without leashes...three pit bulls around him," an eyewitness said.
Eli's owner, who also recorded the suspect walking away, was devastated and frustrated.
Eli was rushed to an animal hospital, but doctors could not save him.
"I just can't believe someone would attack an innocent dog. I don't know what's wrong with people - it's so heartbreaking," dog walker Megan Stafford said.
The suspect is described as a man wearing an orange shirt, orange hat and blue jeans. Officials said he fled the scene after the altercation.
The investigation is ongoing.