The cases involve accusations of fraudulent medical billing, unnecessary procedures and improper insurance reimbursements, with some of the defendants identified as physicians.

Federal agents arrested eight suspects Thursday, with most of the arrests taking place in California, according to Justice Department officials.

Prosecutors allege that the defendants participated in separate schemes designed to obtain substantial payments from Medicare and private insurance companies through fraudulent or medically unjustified claims.

Among the alleged activities were billing private insurers for substance abuse treatments that were not provided, submitting Medicare claims for unnecessary atherectomy procedures and charging the federal health insurance program for hospice services involving patients who were not terminally ill.

Atherectomy is a medical procedure used to remove plaque buildup from blood vessels.

The largest case centers on two individuals based in Los Angeles and another in Texas, who prosecutors accuse of orchestrating a yearslong operation involving patients seeking substance abuse treatment.

According to the Justice Department, the suspects arranged for patients from across the United States to travel to California, where they were allegedly enrolled in health insurance policies for which they did not qualify.

Prosecutors claim the defendants then exploited those insurance arrangements to obtain high reimbursement payments for substance abuse treatment services.

The alleged operation generated more than $1.6 billion in payments, according to federal authorities.

Investigators say the scheme was designed to take advantage of insurance reimbursement systems by using improperly obtained coverage and submitting claims associated with addiction treatment.

Following Thursday’s arrests, five suspects were expected to appear before a federal court in Los Angeles.

Two additional defendants were scheduled to appear in federal court in Texas, while another was expected to make an initial court appearance in Illinois.

The Justice Department did not immediately provide information about legal representation for the defendants.

The charges form part of a broader federal effort to investigate alleged fraud involving government-funded health programs and private insurance providers.

Authorities say the cases illustrate several methods through which health care reimbursement systems can be exploited, including fraudulent patient enrollment, unnecessary medical procedures and billing for services that do not meet eligibility requirements.

The allegations have not yet been proven in court, and the defendants are presumed innocent unless and until found guilty.

Federal prosecutors are expected to pursue the cases through the judicial process as investigators continue examining the alleged financial activities and medical billing practices involved.

The announcement represents a major enforcement action against suspected health care fraud, with approximately $2 billion linked to the schemes identified by federal authorities.