The SCOTUS decision comes from a case where a suspect being questioned in a murder case was read his rights but wouldn't talk other than a grunt or short statement. The cops kept at him, and one of them asked if he believed in God. The guy teared up, and the cop asked him if he asked God for forgiveness after he "shot that boy down". The kid nodded and said he did. A conviction followed.
The appeal said he had invoked his right to remain silent by not saying anything, and that the confession was not admissible. The court disagreed, saying if he didn't want to talk he could have said so. Makes sense to me.
If you're in that position and say anything to the effect of "I want a lawyer" or "I don't want to talk to you guys", the next sounds you'll hear will be pens clicking, notebooks closing, chairs pushing back from the table, and "take this fella back to his cell".