I wouldn't be surprised to see a hung jury. If I was in goal accused of murder I would not tell other prisoners anything about my case, especially not something that would tend to incriminate me and favour the prosecution. I would stick to football, whether I was guilty or innocent. So for me the inmate is not credible.
The police interviews are completely incomprehensible. I can't understand even one whole sentence from either of them. And if people are going to be convicted on their demeanour, can't the detectives be accused of laziness. Who sits like that when interviewing someone?
Anyone could access the house from the rear in the night-time without the neighbour knowing. And where is the knife? They didn't spend much time looking for it. At the very least I would want to see some of the victims' blood on an item of the defendant's clothing. That would be strong evidence, but it doesn't sound as though they found anything.
Having said all that, they will probably convict him.