Dave Bonneau testified Tuesday at a coroner's inquest into the death of Lee Bonneau, who was found with head injuries in a wooded area on the Kahkewistahaw reserve in 2013.
He was last seen walking with an older boy outside the reserve's recreation complex while his foster mother was playing bingo.
Bonneau said the system is faulty and left him in the dark when it came to parental services agreements that his former partner signed.
"Their system is not adequate," he said.
Saskatchewan's children's advocate determined that the 10-year-old boy who killed Bonneau had behavioural issues and probably shouldn't have been in the community unsupervised.
Because he was under 12, he could not be charged under the Youth Criminal Justice Act.
Bonneau told the inquest about the moment he learned his son had been killed and said he has been diagnosed with post-traumatic stress disorder.
"My heart just dropped to my shoes," he said.
On Monday, the coroner's counsel asked Stacey Merk, Lee Bonneau's mother, why social workers had intervened in her family. Lawyer Sonya Guiboche said there were concerns about domestic violence in the home.
Both Bonneau and Merk denied there had been domestic violence.
In a report released last year, children's advocate Bob Pringle said the 10-year-old boy who killed Bonneau didn't receive the help he needed.
Pringle said his investigation found nine child protection concerns reported to the Yorkton Tribal Council Child and Family Services, but as far his office could determine, two concerns were never investigated. Investigation on some of the others was delayed by months, he said.
He also said the RCMP had alerted the agency to the boy's behavioural issues. Mounties believed he was involved in a break and enter in May 2011 when a pregnant dog and her unborn pups were killed.
The inquest is set to run for two weeks in Regina.