A Melbourne man frustrated by his girlfriend's delay in buying him drugs and suspicious she was having sex with their dealer, beat her baby before putting him to sleep.
Hours later, little Silas Leithhead was found "stone cold" in his cot. He was dead just a week after his first birthday.
Paul Ta-Vuong, 31, was on Thursday jailed for 25 years over the brutal attack, which had two victims in mind.
"You used this tiny, dependent and defenceless child to vent your anger towards his mother," Victorian Supreme Court Justice Karin Emerton said.
Ta-Vuong met Silas' mum while they were in rehab for heroin addiction and they soon resumed their use of the drug.
On the day of the murder, May 15 last year, she left their Richmond flat several times to do errands and buy heroin.
"This was frustrating you because she often took quite a long time to score," Justice Emerton said, recounting witness testimony.
"Your suspicions were aroused because you thought she was either `f***ing the dealer or f***ing around with the dealer`."
The attacks on Silas occurred during his mother's absences and Ta-Vuong wrapped the baby for bed while he was dying or already dead.
The couple used the drugs on the mother's return and did not check on Silas for several hours.
"She found him still wrapped up on his back in the centre of the cot. Silas could not be roused and was stone cold. In fact, he was dead," Justice Emerton said.
Ta-Vuong told police the injuries were caused by rough play and then changed his story to a bathroom slip while holding the baby.
The jury rejected that such injuries - skull fractures, a lacerated liver and broken ribs - could be accidental.
Justice Emerton said Ta-Vuong did not divert from his claim it was accidental and so displayed a lack of remorse.
"I am satisfied beyond reasonable doubt Silas suffered multiple violent impacts at your hands, including at least one very severe impact to his head."
Ta-Vuong sat silently in the dock and showed little reaction as his sentence was read out.
He must serve a non-parole period of 20 years.
