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B. At least two elements were operative in the arrest of Toy, and the government need not and does not attempt to rely on either element alone to show that the officers acted reasonably.
1. The first factor was the statement of Hom Way to the agents that he had obtained an ounce of heroin the night before from Toy. The agent had known Hom Way for six weeks and therefore had a basis for judging whether, under arrest, he would be likely to tell the truth or attempt to throw the agents off the scent. An investigator must have leeway to make an informed judgment as to the character of the persons with whom he must deal. Hom Way's designation of petitioner was not vitiated by the fact that Hom Way was himself under arrest; indeed, his statements, which were quite detailed, could be viewed with more confidence since he must have known that he could and would be confronted with any inconsistencies that might develop.
2. The second element is what occurred at Toy's place. The officers did not go to the door in a group, as would have been the case had an arrest been intended on the basis of Hom Way's statement alone; one officer went to investigate further by interviewing Toy, while the others remained nearby. The hour was early, 6:30 a.m., but it was daylight, not darkness. Moreover, the officers were on the trail of heroin, which is easily concealed or destroyed; word of Hom Way's arrest or even of his disappearance from his ordinary haunts could travel quickly.
The officer knocked, and when Toy opened the door, the agent began by asking for laundry. When Toy
