Generally speaking, it's a police officer employed by the state. For instance, you may have city officer, county officers, and state troopers. In my state, state troppers are charged with "enforcing federal and state laws relating to traffic, investigating accidents, and criminal interdiction on roads and highways."
Yes,a state police can investigate a state case.
Maryland State Police was created in 1921.
to be a police officer you need to attend a state approved police academy and be state certified in the state you live in.
In a police state, the government would control the actions of police.
It was the Pennsylvania State Police.
Oregon State Police was created in 1931.
Massachusetts State Police was created in 1865.
Illinois State Police was created in 1922.
Maine State Police was created in 1921.
Indiana State Police was created in 1933.
Louisiana State Police was created in 1922.
Idaho State Police was created in 1919.