At least 78 people died when the fishing vessel flipped and capsized in international waters south-west of Greece early on Wednesday.
A migrant charity says a person they were in contact with on the boat said it was in distress, but Greek authorities say it repeatedly refused offers of help.
Passengers paid $4,500 for passage to Italy, the two Greek sources said.
Aerial photos of the vessel taken by the Greek coastguard hours before the tragedy unfolded showed a vessel crammed with people on its exposed decks.
When the boat reported engine failure and stalled, a coastguard vessel shadowing them came closer.
Persons:
Stelios Misinas, Nikos Alexiou, Adriana Tidona, Tidona, Karolina Tagaris, Michele Kambas, Alex Richardson
Organizations:
Hellenic Coast Guard, REUTERS, Greek coastguard, . Authorities, Greece's coastguard, EU, Amnesty International, coastguard, Thomson
Locations:
Greece, Kalamata, Stelios Misinas KALAMATA, LIBYA, Tobruk, Libya, Italy