VOLUSIA COUNTY, Fla. — Volusia County Animal Services on Thursday euthanized the two dogs that attacked and killed 8-year-old Michael Millett on Jan. 13, county officials announced.

Millett was riding his bicycle with a friend near Arabesque Drive and Airport Road, just north of DeLand, stopped to pet one of the dogs and was then brutally attacked, Volusia County Sheriff Mike Chitwood said the day after the attack. Volusia County Animal Services captured and confiscated both dogs after the incident. Chitwood said the dogs’ owner would be held responsible.

There were no previous reports about the dogs, identified as a pit bull terrier and a herding breed mixed, authorities said. State law therefore required a mandatory 10-business-day quarantine period before euthanasia could proceed without authorization from the owner. During that time, the dogs’ owner could have either relinquished ownership of the dogs or appealed the decision to put them down, but officials were not contacted, they said.

Forensic evidence was sent to Harvard’s Canine Brain Research Group to advance the study of aggressive behaviors in canines to try to improve public safety in the future, Volusia County officials said.

The county said the incident is an example of the importance of reporting potential threats to authorities. In his initial news conference about the attack, Chitwood said residents told investigators that the dogs typically roamed around the neighborhood and were aggressive. Residents said the dogs had terrorized the neighborhood, but no one ever called to make a complaint, according to Chitwood.