There is no word for murders so specific as a nurse killing young healthy patients who are hospitalized for surgery, or the murder of a homeless man. What is the word for murder committed during terroristic acts? It is called homicide or murder.
Perhaps the closest answer to your specific query is going postal:
Going postal, in American English slang, means becoming extremely and uncontrollably angry, often to the point of violence, usually in a workplace environment.
The expression derives from a series of incidents from 1983 onward in which United States Postal Service (USPS) workers shot and killed managers, fellow workers, and members of the police or general public in acts of mass murder. Between 1986 and 1997, more than 40 people were gunned down by spree killers in at least 20 incidents of workplace rage.
Edmond, Oklahoma in 1986
On August 20, 1986, 14 employees were shot and killed and six wounded at the Edmond, Oklahoma, post office by Patrick Sherrill, a postman who then committed suicide with a shot to the forehead. This incident is believed to have coined the term "going postal".
December 31, 1993 in Los Angeles Times:
...the more deadly mass shootings around the nation, which have lent a new term to the language, referring to shooting up the office as "going postal".