It was the second Lynnwood animal cruelty case involving pit bulls in the past month.
The man found one dog limp and the other struggling, police spokeswoman Shannon Sessions said in a statement.
The dog owner, who was not identified, said he tried to help the struggling dog but it bit him in its panic. He ran back inside to get something to cut the rope and when he returned both dogs were dead.
Killed were Peanut, a 1-year-old male, and Wiggles, a 10-month-old female.
The case is under investigation.
On June 28, a young pit bull was hurt and dumped in a trash bin at the Woodland Park Apartments. A passer-by heard the dog and it was rescued, treated at an animal hospital and has been released to a foster home.
Lynnwood police said it's too soon to know if the cases are connected but that possibility is under investigation.
A total reward of $5,000 has been offered for the arrest and conviction of those responsible for the June 28 case.