Final answer:
The law enforcement agency should obtain a search warrant before conducting a thorough search of the apartment to ensure the legality and admissibility of evidence in court.
Step-by-step explanation:
In the scenario where one of three roommates discovers the body of the second roommate with a bloody baseball bat beside his body, the law enforcement agency would be best served by obtaining a search warrant before entering the apartment. This action is necessary to ensure the search is legally sound and evidence collected will be admissible in court. According to the Fourth Amendment, law enforcement is required to obtain a search warrant signed by a judge before engaging in a search or seizure. The warrant provides legal permission to search and/or seize persons or property. Moreover, based on Georgia v. Randolph, police cannot conduct a warrantless search when an occupant objects, even if another consents. In the absence of the third roommate, obtaining consent from the present roommate does not guarantee an unchallenged search.
If there is immediate concern for officer safety, such as a potential threat from further weapons on the premises, they may enter to ensure there are no further immediate threats, which falls under exigent circumstances. However, for a full search of the crime scene, a warrant would typically be required to avoid any allegations of an unlawful search, especially if consent from the third roommate who is absent cannot be obtained.