A jury has found Surender Mehrok guilty of the manslaughter – but not murder – of a 14-week-old baby who was in his care.

Baby Royal, Richard Royal Arif Te Kakahi Winiata Uddin, died in Tauranga on June 7, 2016, of head injuries that have been described as catastrophic and horrific.

Surender Singh Mehrok, 24, faced trial for murder in the High Court at Hamilton and the jury started deliberations late Thursday morning.

The jurors returned with their choice soon after 4pm: not guilty of murder, and guilty of manslaughter.

'There's no dispute that Mr Mehrok caused baby Royal's death. He accepts that,” Justice Christine Gordon had told the jury while summing up earlier.

'The issue for you is whether the Crown has proved beyond reasonable doubt that, at the time he killed baby Royal, Mr Mehrok had the necessary intent for murder.”

Mehrok boarded in the house where baby Royal and his mother stayed, and looked after him on the night she and others from the Nineteenth Avenue house went to get pizza and check a bank balance.

Another boarder said baby Royal started crying after about 10 minutes, and wouldn't settle despite Mehrok making him a bottle and walking him around.

The others returned after about half an hour, to find baby Royal wasn't breathing – and a paediatrician who treated him at nearby Tauranga Hospital believes he died at home.

The Crown had proposed Mehrok 'lost his rag” and decided to take the anger out on baby Royal in increasingly intense assaults.

The defence had said he wasn't thinking and had an impulsive, explosive reaction to a stressful situation.

The Crown highlighted two possible types of murderous intent: either that Mehrok intended to kill baby Royal, or knew his actions could kill or were likely to, and went ahead anyway.

'What was his state of mind?” Justice Gordon asked the jury.

Points of contention in the trial included how many blows caused the injuries seen on baby Royal, and whether he hit the bed or wall first when thrown.

Baby Royal's skull was described as being shattered, and there were two clusters of complex fractures: one on the right side of his head, and the worst at the flattened back of his skull.

A five-year-old witness had consistently described baby Royal hitting the bed first, Crown Prosecutor Kieran Raftery​​ QC said in closing.

That would absorb force, medical experts had said, and wouldn't cause such severe injuries.

A weave pattern on the back of baby Royal's head also suggested he'd struck the carpet.

Therefore, Raftery argued, there was another serious assault which the five-year-old hadn't seen.

However, defence counsel Rob Stevens said there was no need to speculate when there was an eyewitness to the fatal assault.

He argued that the baby was thrown straight into the wall, then fell onto the bed, saying that's what the five-year-old described in cross-examination.

None of the medical experts could rule out one blow causing all the injuries, he said.

There was no evidence of earlier assaults in the bedroom, he said, and just seconds between what was likely the baby vomiting and Mehrok's reaction.

Mehrok probably wasn't thinking at all, Stevens said.

The jury of 12 was given a series of questions to help reach a verdict, and told it must be unanimous.

'Possibly, maybe, probably, likely, very likely are all not good enough when it comes to proof beyond reasonable doubt,” Justice Gordon told them.

Mehrok will be sentenced on October 15 in Tauranga.

-Stuff/Libby Wilson.