Every episode seems to indicate someone different. Although I thought that Abhi might have accidentally removed the rose petal, it would mean that Kajal was accidentally killed as well because anyone could have been fed the kheer. So, if Kajal was purposely killed, then it has to be someone who knew what she and Vandana were up to and was aware of which bowl had the diamond - eliminating Abhi as a suspect.
Also, they showed that someone was roaming around at night, it definitely couldn't have been Abhi, so it's definitely someone else. Who??? (isn't that the million dollar question right now😆)