The accused firebug, who has not yet been charged, first entered the US illegally at the Arizona border in 2018, but was nabbed just days later and shipped back home.

He later crossed the border again, dodging federal agents and finding his way north to the five boroughs — although it is unclear how long he was in the city before the horrific F train attack Sunday, the sources said.

What is clear is that by April 2023 he was staying at a Days Inn hotel on 36th Street which had been converted into a migrant shelter — the first of four tax-funded facilities in the city.

When he was issued a transit ticket in 2023, he gave an address of a shelter on Randall’s Island, the sources said.

On Sunday, police said he was at the 34th Street-Herald Square subway station, calmly watching the sleeping passenger he allegedly set on fire as she apparently burned to death.

Dramatic video obtained by The Post shows cops swarming the fiery scene, with the migrant getting up and walking away.

But cops nabbed him and took him into custody.

Law enforcement sources said the illegal firebug is being held pending autopsy results on the victim.

Manhattan prosecutors are now awaiting word on whether the flames caused the woman’s death — which could mean murder charges against the suspect.

The suspect does not appear to have any other previous criminal history, sources said.

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