A recently released convicted felon was allowed to accompany 20 elementary school fourth graders as a chaperone on a trip to a skating rink late last month, the Seattle Post-Intelligencer reports. Lowell Elementary School in Seattle, Washington, endured a 90 minute lockdown after it was learned that Donald Vassar - a parent of one of the female children in the class - had a history of assault and drug arrests, and was released from prison in February. A warrant had been issued for him in late November after he violated terms of his parole. During the trip, another parent recognized Vassar from a Washington's Most Wanted list, prompting Vassar to flee, although he eventually turned himself in. Gregory King, Lowell's principal, told the news source that it's school policy to perform a verified check of each chaperone's criminal history. Also, district policy mandates volunteers be screened for criminal behavior if they will have regular unsupervised access to children. "Ideally, we would do background checks on everybody," district spokeswoman Teresa Wippel told the news source. "That is the optimal way to do things. But there are going to be cases where that's not going to be practical. And state law doesn't require it." The Seattle Times adds that Vassar goes under a number of aliases, which could explain why Lowell's check didn't turn up any red flags.