What are the circumstances for finding a murder confession coerced?

In Reck v. Pate (1961) 367 U.S. 433 [6 L.Ed.2d 948], also cited by defendant, the circumstances for finding a murder confession coerced were that the 19-year-old, developmentally disabled defendant, with no prior criminal record or experience with the police, was arrested on a Wednesday at 11:00 a.m. (on suspicion of bicycle theft) and was kept in custody for a week without a court hearing. (Id. at pp. 435-436, 441-442.) He did not make incriminating admissions about the murder until Saturday afternoon, when he was confronted with his accomplices who had confessed and implicated him. He then admitted he was present at the crime but said he did not strike the victim. (Id. at p. 438.) On Saturday evening, he participated in a "joint confession" with the other defendants.

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