Next the sisters turned to criminal mischief. Due to their criminal behavior and social disorder they were sent to a high security mental facility, Broadmoor Hospital, where they spent 14 years.
After their novels failed to get any notice, the twins started committing crimes. They committed petty theft, choked each other, and even burned a building down to the ground. They were eventually brought to court on the charge of arson. The judge ruled that since the twins were suffering from a severe social disorder they were to be confined to a high-security mental facility. The twins were sent to Broadmoor Hospital where they remained for the next fourteen years. Their case attained a modicum of notoriety when journalist Marjorie Wallace covered it for The Sunday Times.
In the hospital, the behavior of the sisters puzzled the doctors. They took turns eating. One day one of them would gorge herself while the other starved, and the next day they would switch roles. The sisters were housed in different cells at opposite ends of the hospital, but the nurses often found them frozen in the same bizarre poses.
During their stay in the hospital they made a pact that one of them would die. When the doctors decided to transfer the twins to Caswell Clinic, Jennifer died in transit. Her death remains an unsolved mystery to this day.