Old Saybrook — One person was arrested Tuesday and another is at large in connection with a “shaken baby syndrome” investigation that started in September.

Crystal Dorothy, 26, of 2 Second Ave., Old Saybrook, was charged with risk of injury to a minor, second-degree providing a false statement, second-degree conspiracy to commit a false statement, interfering with an officer and conspiracy to commit interfering with an officer.

Dorothy’s boyfriend, Keith Loftus, 31, is at large and is accused of allegedly causing the injuries that seriously injured the then 7-month-old infant. Police said Loftus is not the child’s father. The child is now in foster care.

Old Saybrook police said the investigation into the abuse allegation began on Sept. 16 when the Yale-New Haven Children’s Hospital alerted the Department of Children and Families about the suspected child abuse.

Police said that Loftus was the child’s caretaker while Dorothy worked. The investigation uncovered that the infant was injured over multiple days in September in Old Saybrook and Deep River while in Loftus’ care.

Police said Loftus and Dorothy fabricated how the injuries occurred to the infant. Police said their story was not consistent with the life-threatening injuries the infant sustained.

Police said officials at DCF, Yale-New Haven Hospital, state police and Middletown Superior Court were involved in the investigation.

Dorothy was held in lieu of a $100,000 bond pending her arraignment Tuesday in Middletown Superior Court.

Old Saybrook police are seeking the public’s assistance in locating Loftus. His last known address is in Deep River, but he is known to frequent Middletown, Old Saybrook and Essex.

Loftus is expected to be charged with first-degree assault, risk of injury to a minor, interfering with an officer, conspiracy to commit interfering with an officer and conspiracy to commit a false statement.

Loftus has an extensive criminal record with convictions for possession of drugs and theft dating back to 2004.

When arrested, he will be held in lieu of a $150,000 bond, police said.

Anyone with information is asked to call Old Saybrook police at (860) 395-3142.