The corpse was discovered in an area of dense woodland on Saturday afternoon, about a 20 minute walk away from where Alice's body was found last Tuesday.
Police say Mr Zalkalns' death was 'consistent with hanging' and there was "no evidence of any third party involvement".
Alice, from Hanwell in west London, disappeared on 28 August and her body was found in the River Brent on 30 September.
Police said significant efforts had been made to conceal it.
Questions have now been raised why the area where Mr Zalkalns body was found had not been searched earlier.
However, police say the search for both Alice and Mr Zalkalns has been 'one of the most complex in recent times'.
Outlining the search strategy, a police spokesman said, "A systematic search had been conducted of 25 square kilometres of canals, rivers and land. The searches considered all possible evidential opportunities, based upon the search strategy agreed as part of the investigation.
"Over the weekend of 27/28 September this search was expanded again to include open space searches utilising regular officers and mounted branch. These searches expanded south and west from Trumpers Way for a further eight square kilometres including Boston Manor Park and Osterley Park.
"These initial visual searches of open land highlighted inaccessible areas that required further search with specialist equipment, trained officers, police divers or search dogs.
"A number of the areas identified for further search were within Boston Manor Park.
"The densely overgrown area where Arnis Zalkalns was discovered was one of these areas. This area had not been searched by police previously.
"This search commenced on Saturday 4 October and at approximately 2pm the body of Arnis Zalkalns was found.
"The recovery required a substantial removal of forestry to enable access for forensic teams. The body was eventually removed shortly after 10am on Sunday 5 October. "
