The vandalism early Monday morning caused more than $8,000 in damage to the iconic park on the north end of Lake Union.
But investigators got a tip that a large group spotted running from the park that morning had gathered to celebrate the 19-year-old's birthday.
Detectives went to the man's home Thursday where he admitted he had tagged walls at the park, police said. He's been booked into the King County Jail for investigation of malicious mischief. Investigators say the suspect has a history of vandalism.
Seattle police say they are still looking for other suspects in the case and ask anyone with tips to call 206-684-5534.