I read that population 3 are metal poor stars especially those very very massive ones will quickly exhaust their fuel and goes into supernovae when their internal pressure drops due to pair instability. They claims these stars only exists in the early universe which may be the ancestors of all other stars we see today's, nevertheless they also claimed we should be able to observed them in red shifted galaxies like going backward in time. So I wonder how can we tell them apart from population 1 and 2 stars? Is it difficult to identify them which is probably why we haven't observed any of those?
Population 3 stars can be distinguished from population 1 and 2 stars by the absence of metal in the stars light spectra. Even when the light is red shifted, emission and absorption lines can still be seen.