In the Vietnam war, 144 POWs died. According to documents released to the ACLU there were 190 deaths of detainees in the War on Terror (not all at Guantanamo).

… a detainee was killed by an unnamed sergeant who walked into a room
where the detainee was lying wounded “and assaulted him … then shot
him twice thus killing him,” one of the investigating documents says.
The sergeant than instructed the other soldiers present to lie about the incident.
Later, the document says an unnamed corporal then shot the deceased
detainee in the head after finding his corpse.

It’s horrific that for decades we thought of the treatment of POWs in Vietnam as the epitome of brutality but more prisoner’s died in our custody then in Vietnamese custody!

The defense department defends it as not being as bad as it sounds and that people have been convicted of murder:

The Defense Department disputes the allegations, saying it
takes detainee treatment seriously.

Some history:

guantanomo