Meaning of 的 in 只有三个得满分的 The full sentence is

他考得很好，得了满分。听说只有三个得了满分的。 

I get a bit confused with 的. I understand that the sentence means “there are only 3 people that get full marks.” 

Please help me out. Thank you guys :D
听说只有三个(考生)得了满分 -- I heard that only three (examinees) got full marks

听说只有三个得了满分的(考生)--  I heard that there are only three (examinees) who got full marks

The object 考生 was omitted

考生 = examinee

得了满分的考生 = examinee who got full mark 

'得了满分的' is an adjectival phrase that describes '考生'