The chief purpose for using informants is
a. to solve crimes that have eluded investigators.
b. to stop crimes before they happen.
c. to entrap known criminals.
d. to provide probable cause for arrests and search warrants.

The chief purpose for using informants is to provide probable cause for arrests and search warrants.

Option: (D)

Explanation:

An informant is the person or group that provides the important information related to the crime. So based on these informants information it is easier for the concerned authority to provide the search and investigation warrants. So, it is very important for the informant to be genuine and trusted. These informants may be eye witness, or criminal informant known as confidential human source.