spill one's guts

spill one's guts (to sb) (to tell everything, and usually in some sort of confession, forced or voluntary; to confess everything) — расколоться; выболтать, проболтаться

For example, if a man is arrested for a crime, he will spill his guts under the intense interrogation of the police

Example: At first, the suspect would not tell us anything about the other participants in the crime. But after being offered a deal, he spilled his guts. (Wictionary)

see also
[crack under pressure]

сf.:
[tip one's hand]
[let something slip] (out)
[spill the beans]
[let the cat out of the bag]