ERIE, Colo. -- Authorities said they are trying to determine how a 4-month-old boy ended up with multiple broken bones at the home of his foster parents.

Mason Blackstock's injuries included seven broken ribs in various stages of healing, a broken forearm and leg with healing malformations and numerous bruises, according to the Boulder Daily Camera newspaper. No arrests have been made.

The newspaper reported a Boulder County judge approved a search warrant for the Erie home of Mark Scollon and Racheal Banta, the infant's foster parents, as part of an investigation into how the boy sustained his injuries. Banta and Scollon have hired an attorney.

Mason, who was born 26 weeks premature, was admitted to the Children's Hospital in Aurora on July 23 with signs of bruising to his arms, chest, chin, ears, neck and back, according to the warrant obtained by the newspaper. He was 4 months old at the time, and his foster parents said they had no explanation of how he was injured, according to the warrant.