This case was a Colorado case regarding searches and seizures outside of the context of an arrest. It is about what sort of search and seizure can be performed when there is a “consensual” interaction between the police and a civilian.
In this case, Herrera was stopped for questioning by the police as he was walking along “in the vicinity” of an abandoned car, carrying a gas can. It was 1:30 in the morning. When the police talked to Herrera, they decided that he was drunk and, under Colorado law, prepared to take him into civil protective custody. In other words, there was no suspicion at this point that Herrera had committed a crime. He was merely being taken into custody for his own protection.
The officers patted Herrera down for weapons and found a pocket knife. They found a clear plastic baggie with what looked like marijuana, but decided to simply dump that out. They then found folded squares of paper. When they opened those, they found that there was cocaine in them. They arrested Herrera and he was eventually convicted.
On appeal, Herrera’s case was remanded for further findings because it was held that the search that the officers conducted went too far. Herrera was not suspected of a crime. The contact with him was consensual. Therefore, the officers had no reason to search him other than to ascertain that he had no weapons and to take his belongings and inventory them so he could get them back when he was released. They found no weapons in the pat down (a pocket knife is not really a serious weapon) and had no further reason to think that he had committed a crime. Even so, they opened the paper squares. There was no reason, the court said, for them to open the squares since that constituted a search that was well beyond what was needed for Herrera’s safety and for inventorying his possessions.
For this reason, the court ruled that the police had gone too far in their search. This helps to clarify what police may or may not do (in Colorado) in the course of a consensual encounter with a civilian.
You can find the judge's opinion on this case here: http://scholar.google.com/scholar_case?case=17703808020899747781&q=People+v.+Herrera,+1+P.3d+234&hl=en&as_sdt=6,48&as_vis=1