My reading of the whole interview thing, is that it appears a police interview can only be used as evidence about the person giving the interview, not anyone else. But if that person then stands up and repeats it in court, with full cross-examination, then it and his evidence on the stand can then be used about all people involved.
Not a lawyer, no legal knowledge, just the best sense I can make out of it all. Very glad to hear it in any case, as Patel's evidence is key; I'm rather surprised the prosecutions didn't cut a deal with him and just use him as a witness, frankly, as it feels a little harsh to charge him with murder given his low involvement. The weapon may well mean he ends up guilty of something but I bet he'd have bitten their hand off to plead guilty for something minor like intent to assault or whatever and then been a full witness. Or perhaps they figured his story would carry more weight if it didn't seem like he's been bought off with a lesser charge?