I'm looking for an idiom or expression for describing someone who fools or manipulates other people by pretending to be poor/ weak or incapacitated/ ill (=unwell)/ inoffensive / innocent as a tactic to reach their aims or goals, because they know that in such conditions, it is more likely that people react more kindly and thus help them to reach what they intended to gain or receive (for example more money, more salary, more help, more support or attention, etc.)
1- Two bully students have been fighting in the playground, when they are called to the pricinpal's office one of them keeps silent, and pretends to be inoffensive and just being beaten and not have beaten the other student, in order that the principal not scold him and only the other student would be blamed and punished.
2- Beggars use this act/ tactic to make people feel pity for them and help them more.
3- Sometimes kids act like this in order not being punished by their parents or teachers.
In Persian we use this idiom " to play dead like a rat/ mouse". (As you know, the mice use this trick as a defense mechanism when facing a threatening situation, and scientifically is called "tonic immobility".)
"Come on! Don't trust him, and don't be fooled by his innocent look either. He is just playing dead like a rat!
"Don't be fooled by her, she is just pretending to have low back pain, she is healthier than anyone in the office! Let her do her own job on her own. She is just playing dead like a rat!"
Is there any idiom or expression that can be used for describing these kind of sly and cunning people who reach their aims or goals by pretending to be weak, poor, inoffensive, innocent,...?
I have found "to play the innocent" but it means "to pretend not knowing something", so I don't think it could be used in those situations too.