KUALA LUMPUR, Nov 7 — Then prime minister Datuk Seri Najib Razak was referred to by the codename "OP” which is "Optimus Prime” in BlackBerry Messenger (BBM) chats in 2014 with his alleged right-hand man and now-fugitive Low Taek Jho, former AmBank banker Joanna Yu told the High Court today.

Yu said this while testifying as the 41st prosecution witness in Najib’s trial, where the former prime minister is facing 25 charges over the misappropriation of 1Malaysia Development Berhad’s (1MDB) RM2.28 billion which were alleged to have entered his personal bank accounts.

Shown transcripts of her BBM chats with Low which were extracted from her phone, Yu was today referred to Low's BBM message on December 8, 2014, which said: "Tell him OP asked to close the account by end December due to his behaviour”.

Asked by lead prosecutor Datuk Seri Gopal Sri Ram on who was "OP” in this BBM message, Yu said: "Um, it's referring to Datuk Seri Najib.”

Sri Ram: What does ‘OP’ actually stand for?

Yu: It's a code name, I remember asking Jho and he said it's Optimus Prime, so it's prime minister.

Sri Ram: ‘OP’ is Optimus Prime and that's the codename for Datuk Seri Najib?

Yu: He told me that, yes.

Sri Ram: I want to ask you, when did you say Jho Low said ‘OP stands for Optimus Prime referring to Datuk Seri Najib’, when was that and by what method he informed you?

Yu: I can't remember, probably Blackberry or over a chat, I can't remember.

Sri Ram: Right, but when this message came to you, ‘tell him OP’, did you have any doubt in your mind who OP was?

Yu: No.

Sri Ram: And in your mind, who was OP?

Yu: Um, Datuk Seri Najib.

Yu did not explain further about Optimus Prime, but it is widely known as a key character in the science fiction Transformers series regarding alien robots.

Najib's trial is being heard by High Court judge Datuk Collin Lawrence Sequerah.