Organization
The camp was divided into two sections - the camp area and the crematorium. The camp area consisted of 32 barracks, including one for clergy imprisoned for opposing the  regime and one reserved for medical experiments. The courtyard between the prison and the central kitchen was used for the summary execution of prisoners. An electrified barbed-wire fence, a ditch, and a wall with seven guard towers surrounded the camp.
In early 1937, the SS, using prisoner labor, initiated construction of a large complex of buildings on the grounds of the original camp. Prisoners were forced to do this work, starting with the destruction of the old munitions factory, under terrible conditions. The construction was officially completed in mid-August 1938 and the camp remained essentially unchanged and in operation until 1945. Dachau thus was the longest running concentration camp of the Third Reich. The area in Dachau included other SS facilities beside the concentration camp - a leader school of the economic and civil service, the medical school of the SS, etc. The KZ at that time was called a "protective custody camp," and occupied less than half of the area of the entire complex.
Dachau also served as the central camp for Christian religious prisoners. According to records of the Roman Catholic Church, at least 3000 religious, deacons, priests, and bishops were imprisoned there.
In August 1944 a women's camp opened inside Dachau. Its first shipment of women came from Auschwitz Birkenau. Only nineteen women guards served at Dachau, most of them until liberation.
In the last war months the conditions at Dachau became even worse. As Allied forces advanced toward Germany, the Germans began to move prisoners in concentration camps near the front to camps further inward. They hoped to prevent the liberation of large numbers of prisoners. Transports from the evacuated camps arrived continuously at Dachau. After days of travel, with little or no food or water, the prisoners arrived weak and exhausted, often near death. Typhus epidemics became a serious problem due to overcrowding, poor sanitary conditions, insufficient provisions, and the weakened state of the prisoners.
Due to continual new transportations from the front the camp was constantly overcrowded, the hygienic conditions were beneath human dignity. Starting from the end of 1944 up to the day of liberation 15,000 people died, about half of all victims in KZ Dachau.
On April 27, 1945, Victor Mauer, delegate of the International Committee of the Red Cross, was allowed to enter camps and distribute food. In the evening of the same day a prisoner transport arrived from Buchenwald. Only 800 survivors were brought from originally 4,480 to 4,800 persons in transit. Over 2,300 corpses were let lie in and around the train. The last regular commander of the KZ, Obersturmbannfuhrer Eduard Weiter, had already fled on 26 April. He probably followed Obersturmbannfuhrer Martin Weiss, who had led the camp from September 1942 until November 1943.
On April 28, 1945, the day before the surrender, Camp Commandant Martin Weiss had left the Dachau camp, along with most of the regular guards and administrators in the camp. On that same day, Victor Maurer, a representative of the Red Cross, had tried to persuade 1st Lt. Johannes Otto, the adjutant of Commandant Weiss, not to abandon the camp, but to leave guards posted to keep the prisoners inside until the Americans arrived. Mauer feared that the prisoners would escape en masse and spread the active typhus fever epidemic. Lt. Otto declined to remain and fled*.
*source: wikipedia.org, ushmm.org