Why did the Supreme Court rule that the confession in Ashcraft v. Tennessee could not be used as evidence?

In Ashcraft v. Tennessee (1944), the Supreme Court ruled that the confession could not be used as evidence because it was obtained through intense psychological pressure. The suspect had been subjected to 36 hours of continuous interrogation under the glare of bright lights. The Court determined that such extreme psychological coercion rendered the confession inadmissible, even in the absence of physical brutality.1