Noah Cownden died just three days before his second birthday. Paramedics arrived at his family's townhouse on April 9, 2008 after receiving a 911 call.
The autopsy showed Cownden suffered a fatal head wound, while in the care of stepfather Streiling.
At the time of the fall, the toddler's death was treated as an accident but four years later, police began a so-called "Mr. Big" sting operation against Streiling.
During his trial, the judge heard undercover officers led Streiling to believe he was being recruited into a gang, that they paid him $10,000, took him for expensive dinners and on ski trips.
When two uniformed officers visited him, telling Streiling he was about to be charged in Cownden's death, the gang promised to protect him if he'd confess to their boss, who was also an undercover officer.
'That's the end of your life'
On Wednesday, Justice Jennifer Power ruled the confession Streiling made to a supposed gang leader during that sting was unreliable, given the amount of police inducement and that medical evidence failed to prove conclusively Cownden's death was the result of an assault, rather than a bathtub slip as Streiling testified.
"He was led to believe very persuasively, 'You're done, that's the end of your life...You're going to prison as a child killer for the rest of your life for a life sentence. Or you can just tell us you did something to him,'" said Streiling's lawyer, Martin Allen.
Crown prosecutors have not yet indicated whether they intend to appeal the verdict.
Cownden's family said they were disappointed, but also relieved the trial is finally over.
"Obviously, we would have liked it to be different. But we respect the process," said Chris Cownden, Noah's father.