Prisons in Iraq held thousands of Islamic State group militants, but few outside the government knew exactly how many. Baghdad-based reporter Qassim Abdul-Zahra set out to find out – and he wasn’t going to take a rough estimate for an answer.

With Baghdad correspondent Susannah George and Mideast enterprise editor Lee Keath, Abdul-Zahara analyzed documents he obtained from a Justice Ministry official, finding that the government was holding at least 19,000 people accused of ISIS connections or other terror-related offenses and that more than 3,000 of them had been sentenced to death.

For their exclusive reporting and analysis, Abdul-Zahra, George and Keath win this week’s Beat of the Week.

When Abdul-Zahra set out on his search for the elusive number, he knew that government spokesmen would not give any numbers. He remembered an official who would be in a position to know and whom he’d seen at public events, so through his contacts, Abdul-Zahra tracked him down and arranged a meeting. The official told Abdul-Zahra that he would only give him approximate figures.

“We don’t want approximate,” Abdul-Zahra said, and asked if he had any documents. The official was hesitant at first. Eventually, Abdul-Zahra was able to meet the official and copy the government files from his laptop.

We don’t want approximate.”

Qassim Abdul-Zahra, to an Iraqi official offering less-than-accurate data on detainees

It turned out to be two files in Arabic: One, a main spreadsheet listing all 27,000-plus prisoners in Iraqi prisons as of late January – with names, the charges they were convicted on, their sentences. The other was a set of individual spreadsheets from each of the 25 prisons run by the federal government.

Keath, with help from Abdul-Zahra, Hamza Hendawi and members of the Cairo bureau, arrived at the number of nearly 9,000 terror convicts in prisons. But this was missing the large number of detainees, those swept up by security agencies in the assault on Mosul and other operations who are still being interrogated but are supposed to go on trial.

Abdul-Zahra was able to get a figure of 11,000 for those held by the Interior Ministry’s intelligence agency alone, putting the overall tally at least 19,000.

Susannah George, who had already reported on conditions in detention centers and knew that the justice system was swamped by these numbers, worked with Abdul-Zahra to pursue interviews on how prisoners are crammed in and how militants mix with other inmates trying to recruit them.

The story ran with difficult-to-obtain photos of detainees from Bram Janssen:

The result was a story showing how officials were struggling with the flood of prisoners, causing some embarrassment for the government. It was cited in Iraqi media – though not on the state-run channel. The Saudi-owned Al-Arabiya TV, one of the main news channels in the region, also ran a segment on the AP report.

Notably, the story was also bounced around among members on pro-ISIS and other militant web forums, mainly garnering comments praying to God to win the prisoners’ release. Human Rights Watch cited the story in a short piece entitled “Rush to Judgment in Iraq Harms Justice.”

For intrepid source work and analysis to establish the facts around the imprisonment of thousands of Islamic State group militants in Iraq, Abdul-Zahra, George and Keath win Beat of the Week.