OMAHA, Neb. (AP) — Prosecutors opened the first-degree murder trial against a former doctor by arguing he committed four Omaha killings to avenge his firing from Creighton University Medical Center.

The prosecutors outlined their case Monday against Anthony Garcia, who is charged with stabbing to death the 11-year-old son of two medical doctors and the family’s housekeeper in 2008 and then killing another Omaha doctor and his wife in 2013. They say the killings were motivated by Garcia’s long-simmering rage from being fired from the medical school’s residency program in 2001.

Deputy County Attorney Brenda Beadle argued, “”This is a case about revenge.”

Garcia’s attorney responded that prosecutors lack witnesses or physical evidence and that their case would fall apart when all the evidence is presented.