But what exactly would stop the FBI from sending agents to Singapore and conducting their own investigation, with or without consent? Need it be covert, it coul

But what exactly would stop the FBI from sending agents to Singapore and conducting their own investigation, with or without consent? Need it be covert, it could certainly be covert. I'm currently operating under the assumption (which seemed likely to me) that the Singaporean government / police had a motive for not wanting to involve the FBI. Hence the more reason for the FBI to be there.